[Qemu-block] [RFC PATCH COLO v2 01/13] docs: block replication's description
Signed-off-by: Wen Congyang Signed-off-by: Paolo Bonzini Signed-off-by: Yang Hongyang Signed-off-by: zhanghailiang Signed-off-by: Gonglei --- docs/block-replication.txt | 147 + 1 file changed, 147 insertions(+) create mode 100644 docs/block-replication.txt diff --git a/docs/block-replication.txt b/docs/block-replication.txt new file mode 100644 index 000..874ed8e --- /dev/null +++ b/docs/block-replication.txt @@ -0,0 +1,147 @@ +Block replication + +Copyright Fujitsu, Corp. 2015 +Copyright (c) 2015 Intel Corporation +Copyright (c) 2015 HUAWEI TECHNOLOGIES CO.,LTD. + +This work is licensed under the terms of the GNU GPL, version 2 or later. +See the COPYING file in the top-level directory. + +The block replication is used for continuous checkpoints. It is designed +for COLO that Secondary VM is running. It can also be applied for FT/HA +scene that Secondary VM is not running. + +This document gives an overview of block replication's design. + +== Background == +High availability solutions such as micro checkpoint and COLO will do +consecutive checkpoint. The VM state of Primary VM and Secondary VM is +identical right after a VM checkpoint, but becomes different as the VM +executes till the next checkpoint. To support disk contents checkpoint, +the modified disk contents in the Secondary VM must be buffered, and are +only dropped at next checkpoint time. To reduce the network transportation +effort at the time of checkpoint, the disk modification operations of +Primary disk are asynchronously forwarded to the Secondary node. + +== Workflow == +The following is the image of block replication workflow: + ++--+++ +|Primary Write Requests||Secondary Write Requests| ++--+++ + | | + | (4) + | V + | /-\ + | Copy and Forward| | + |-(1)--+ | Disk Buffer | + | | | | + | (3) \-/ + | speculative ^ + |write through(2) + | | | + V V | + +--+ ++ + | Primary Disk | | Secondary Disk | + +--+ ++ + +1) Primary write requests will be copied and forwarded to Secondary + QEMU. +2) Before Primary write requests are written to Secondary disk, the + original sector content will be read from Secondary disk and + buffered in the Disk buffer, but it will not overwrite the existing + sector content in the Disk buffer. +3) Primary write requests will be written to Secondary disk. +4) Secondary write requests will be buffered in the Disk buffer and it + will overwrite the existing sector content in the buffer. + +== Architecture == +We are going to implement COLO block replication from many basic +blocks that are already in QEMU. + + virtio-blk || + ^||.-- + |||| Secondary +1 Quorum ||'-- + / \ || +/\|| + Primary 2 NBD ---> 2 NBD + disk client|| server virtio-blk + ||^ ^ +. ||| | +Primary | || Secondary disk <- hidden-disk 4 <- active-disk 3 +' ||| backing^ backing + ||| | + ||| | + ||'-' + || drive-backup sync=none + +1) The disk on the primary is represented by a block device with two +children, providing replication between a primary disk and the host that +runs the secondary VM. The read pattern for quorum can be extended to +make the primary always read from the local disk instead of going through +NBD. + +2) The secondary disk receives writes from the primary VM through QEMU's +embedded NBD server (speculative write-through)
Re: [Qemu-block] [RFC PATCH COLO v2 01/13] docs: block replication's description
On 03/25/2015 03:36 AM, Wen Congyang wrote: > Signed-off-by: Wen Congyang > Signed-off-by: Paolo Bonzini > Signed-off-by: Yang Hongyang > Signed-off-by: zhanghailiang > Signed-off-by: Gonglei > --- > docs/block-replication.txt | 147 > + > 1 file changed, 147 insertions(+) > create mode 100644 docs/block-replication.txt > Grammar review only (I'll leave the technical review to others) > diff --git a/docs/block-replication.txt b/docs/block-replication.txt > new file mode 100644 > index 000..874ed8e > --- /dev/null > +++ b/docs/block-replication.txt > @@ -0,0 +1,147 @@ > +Block replication > + > +Copyright Fujitsu, Corp. 2015 > +Copyright (c) 2015 Intel Corporation > +Copyright (c) 2015 HUAWEI TECHNOLOGIES CO.,LTD. Space after comma in English writing. > + > +This work is licensed under the terms of the GNU GPL, version 2 or later. > +See the COPYING file in the top-level directory. > + > +The block replication is used for continuous checkpoints. It is designed Sounds better as either of: The block replication feature is... Block replication is... > +for COLO that Secondary VM is running. It can also be applied for FT/HA Please define COLO and FT/HA on first use (okay to abbreviate elsewhere in the document, but the first use should not assume the acronym is well-known) s/for COLO that/for COLO (COurse-grain LOck-stepping), where the/ > +scene that Secondary VM is not running. s/for FT/HA scene that/for the FT/HA (Fault-tolerance/High Assurance) scenario, where the/ > + > +This document gives an overview of block replication's design. > + > +== Background == > +High availability solutions such as micro checkpoint and COLO will do > +consecutive checkpoint. The VM state of Primary VM and Secondary VM is s/checkpoint/checkpoints/ > +identical right after a VM checkpoint, but becomes different as the VM ... > + > +4) The hidden-disk is created automatically. It buffers the original content > +that is modified by the primary VM. It should also be an empty disk, and > +the dirver supports bdrv_make_empty(). s/dirver/driver/ > + > +== New block driver interface == > +We add three block driver interfaces to control block replication: > +a. bdrv_start_replication() > + Start block replication, called in migration/checkpoint thread. > + We must call bdrv_start_replication() in secondary QEMU before > + calling bdrv_start_replication() in primary QEMU. > +b. bdrv_do_checkpoint() > + This interface is called after all VM state is transfered to s/transfered/transferred/ > + Secondary QEMU. The Disk buffer will be dropped in this interface. > + The caller must hold the I/O mutex lock if it is in migration/checkpoint > + thread. > +c. bdrv_stop_replication() > + It is called when failover. We will flush the Disk buffer into s/when/on/ > + Secondary Disk and stop block replication. The vm should be stopped > + before calling it. The caller must hold the I/O mutex lock if it is > + in migration/checkpoint thread. > + > +== Usage == > +Primary: > + -drive if=xxx,driver=quorum,read-pattern=fifo,\ > + children.0.file.filename=1.raw,\ > + children.0.driver=raw,\ > + children.1.file.driver=nbd+colo,\ > + children.1.file.host=xxx,\ > + children.1.file.port=xxx,\ > + children.1.file.export=xxx,\ > + children.1.driver=raw,\ > + children.1.ignore-errors=on This command line looks like multiple arguments because of the leading whitespace on succeeding lines. I don't know if there is any better way to format it, though, to make it obvious that it is all a single argument to -drive. > + Note: > + 1. NBD Client should not be the first child of quorum. > + 2. There should be only one NBD Client. > + 3. host is the secondary physical machine's hostname or IP > + 4. Each disk must have its own export name. Maybe a note 5 to call out the formatting aspect of the command line? > + > +Secondary: > + -drive if=none,driver=raw,file=1.raw,id=nbd_target1 \ > + -drive if=xxx,driver=qcow2+colo,file=active_disk.qcow2,export=xxx,\ > + backing_reference.drive_id=nbd_target1,\ > + backing_reference.hidden-disk.file.filename=hidden_disk.qcow2,\ > + backing_reference.hidden-disk.driver=qcow2,\ > + backing_reference.hidden-disk.allow-write-backing-file=on > + Then run qmp command: > +nbd_server_start host:port > + Note: > + 1. The export name for the same disk must be the same in primary > + and secondary QEMU command line > + 2. The qmp command nbd_server_start must be run before running the > + qmp command migrate on primary QEMU > + 3. Don't use nbd_server_start's other options > + 4. Active disk, hidden disk and nbd target's length should be the > + same. > + 5. It is better to put active disk and hidden disk in ramdisk. > -- Eric Blake eblake redhat com+1-919-301-3266 Libvirt
Re: [Qemu-block] [RFC PATCH COLO v2 01/13] docs: block replication's description
On Wed, 03/25 17:36, Wen Congyang wrote: > Signed-off-by: Wen Congyang > Signed-off-by: Paolo Bonzini > Signed-off-by: Yang Hongyang > Signed-off-by: zhanghailiang > Signed-off-by: Gonglei > --- > docs/block-replication.txt | 147 > + > 1 file changed, 147 insertions(+) > create mode 100644 docs/block-replication.txt > > diff --git a/docs/block-replication.txt b/docs/block-replication.txt > new file mode 100644 > index 000..874ed8e > --- /dev/null > +++ b/docs/block-replication.txt > @@ -0,0 +1,147 @@ > +Block replication > + > +Copyright Fujitsu, Corp. 2015 > +Copyright (c) 2015 Intel Corporation > +Copyright (c) 2015 HUAWEI TECHNOLOGIES CO.,LTD. > + > +This work is licensed under the terms of the GNU GPL, version 2 or later. > +See the COPYING file in the top-level directory. > + > +The block replication is used for continuous checkpoints. It is designed > +for COLO that Secondary VM is running. It can also be applied for FT/HA > +scene that Secondary VM is not running. > + > +This document gives an overview of block replication's design. > + > +== Background == > +High availability solutions such as micro checkpoint and COLO will do > +consecutive checkpoint. The VM state of Primary VM and Secondary VM is > +identical right after a VM checkpoint, but becomes different as the VM > +executes till the next checkpoint. To support disk contents checkpoint, > +the modified disk contents in the Secondary VM must be buffered, and are > +only dropped at next checkpoint time. To reduce the network transportation > +effort at the time of checkpoint, the disk modification operations of > +Primary disk are asynchronously forwarded to the Secondary node. > + > +== Workflow == > +The following is the image of block replication workflow: > + > ++--+++ > +|Primary Write Requests||Secondary Write Requests| > ++--+++ > + | | > + | (4) > + | V > + | /-\ > + | Copy and Forward| | > + |-(1)--+ | Disk Buffer | > + | | | | > + | (3) \-/ > + | speculative ^ > + |write through(2) > + | | | > + V V | > + +--+ ++ > + | Primary Disk | | Secondary Disk | > + +--+ ++ > + > +1) Primary write requests will be copied and forwarded to Secondary > + QEMU. > +2) Before Primary write requests are written to Secondary disk, the > + original sector content will be read from Secondary disk and > + buffered in the Disk buffer, but it will not overwrite the existing > + sector content in the Disk buffer. Could you elaborate a bit about the "existing sector content" here? IIUC, it could be from either "Secondary Write Requests" or previous COW of "Primary Write Requests". Is that right? > +3) Primary write requests will be written to Secondary disk. > +4) Secondary write requests will be buffered in the Disk buffer and it > + will overwrite the existing sector content in the buffer. > + > +== Architecture == > +We are going to implement COLO block replication from many basic > +blocks that are already in QEMU. > + > + virtio-blk || > + ^||.-- > + |||| Secondary > +1 Quorum ||'-- > + / \ || > +/\|| > + Primary 2 NBD ---> 2 NBD > + disk client|| server >virtio-blk > + ||^ > ^ > +. ||| > | > +Primary | || Secondary disk <- hidden-disk 4 > <- active-disk 3 > +' ||| backing^ backing > + ||| | > + ||| | > + ||'-' > + || drive-backup sync=no
Re: [Qemu-block] [RFC PATCH COLO v2 01/13] docs: block replication's description
On 03/26/2015 02:31 PM, Fam Zheng wrote: > On Wed, 03/25 17:36, Wen Congyang wrote: >> Signed-off-by: Wen Congyang >> Signed-off-by: Paolo Bonzini >> Signed-off-by: Yang Hongyang >> Signed-off-by: zhanghailiang >> Signed-off-by: Gonglei >> --- >> docs/block-replication.txt | 147 >> + >> 1 file changed, 147 insertions(+) >> create mode 100644 docs/block-replication.txt >> >> diff --git a/docs/block-replication.txt b/docs/block-replication.txt >> new file mode 100644 >> index 000..874ed8e >> --- /dev/null >> +++ b/docs/block-replication.txt >> @@ -0,0 +1,147 @@ >> +Block replication >> + >> +Copyright Fujitsu, Corp. 2015 >> +Copyright (c) 2015 Intel Corporation >> +Copyright (c) 2015 HUAWEI TECHNOLOGIES CO.,LTD. >> + >> +This work is licensed under the terms of the GNU GPL, version 2 or later. >> +See the COPYING file in the top-level directory. >> + >> +The block replication is used for continuous checkpoints. It is designed >> +for COLO that Secondary VM is running. It can also be applied for FT/HA >> +scene that Secondary VM is not running. >> + >> +This document gives an overview of block replication's design. >> + >> +== Background == >> +High availability solutions such as micro checkpoint and COLO will do >> +consecutive checkpoint. The VM state of Primary VM and Secondary VM is >> +identical right after a VM checkpoint, but becomes different as the VM >> +executes till the next checkpoint. To support disk contents checkpoint, >> +the modified disk contents in the Secondary VM must be buffered, and are >> +only dropped at next checkpoint time. To reduce the network transportation >> +effort at the time of checkpoint, the disk modification operations of >> +Primary disk are asynchronously forwarded to the Secondary node. >> + >> +== Workflow == >> +The following is the image of block replication workflow: >> + >> ++--+++ >> +|Primary Write Requests||Secondary Write Requests| >> ++--+++ >> + | | >> + | (4) >> + | V >> + | /-\ >> + | Copy and Forward| | >> + |-(1)--+ | Disk Buffer | >> + | | | | >> + | (3) \-/ >> + | speculative ^ >> + |write through(2) >> + | | | >> + V V | >> + +--+ ++ >> + | Primary Disk | | Secondary Disk | >> + +--+ ++ >> + >> +1) Primary write requests will be copied and forwarded to Secondary >> + QEMU. >> +2) Before Primary write requests are written to Secondary disk, the >> + original sector content will be read from Secondary disk and >> + buffered in the Disk buffer, but it will not overwrite the existing >> + sector content in the Disk buffer. > > Could you elaborate a bit about the "existing sector content" here? IIUC, it > could be from either "Secondary Write Requests" or previous COW of "Primary > Write Requests". Is that right? Yes. > >> +3) Primary write requests will be written to Secondary disk. >> +4) Secondary write requests will be buffered in the Disk buffer and it >> + will overwrite the existing sector content in the buffer. >> + >> +== Architecture == >> +We are going to implement COLO block replication from many basic >> +blocks that are already in QEMU. >> + >> + virtio-blk || >> + ^||.-- >> + |||| Secondary >> +1 Quorum ||'-- >> + / \ || >> +/\|| >> + Primary 2 NBD ---> 2 NBD >> + disk client|| server >> virtio-blk >> + ||^ >> ^ >> +. ||| >> | >> +Primary | || Secondary disk <- hidden-disk 4 >> <- active-disk 3 >> +' ||| backing^ >> backing >> + ||| | >> + ||
Re: [Qemu-block] [RFC PATCH COLO v2 01/13] docs: block replication's description
On 03/25/2015 11:38 PM, Eric Blake wrote: > On 03/25/2015 03:36 AM, Wen Congyang wrote: >> Signed-off-by: Wen Congyang >> Signed-off-by: Paolo Bonzini >> Signed-off-by: Yang Hongyang >> Signed-off-by: zhanghailiang >> Signed-off-by: Gonglei >> --- >> docs/block-replication.txt | 147 >> + >> 1 file changed, 147 insertions(+) >> create mode 100644 docs/block-replication.txt >> > > Grammar review only (I'll leave the technical review to others) > >> diff --git a/docs/block-replication.txt b/docs/block-replication.txt >> new file mode 100644 >> index 000..874ed8e >> --- /dev/null >> +++ b/docs/block-replication.txt >> @@ -0,0 +1,147 @@ >> +Block replication >> + >> +Copyright Fujitsu, Corp. 2015 >> +Copyright (c) 2015 Intel Corporation >> +Copyright (c) 2015 HUAWEI TECHNOLOGIES CO.,LTD. > > Space after comma in English writing. Yes, but I am not sure I can change it. HUAWEI always use this way. You can find it in bootdevice.c Thanks Wen Congyang > >> + >> +This work is licensed under the terms of the GNU GPL, version 2 or later. >> +See the COPYING file in the top-level directory. >> + >> +The block replication is used for continuous checkpoints. It is designed > > Sounds better as either of: > The block replication feature is... > Block replication is... > >> +for COLO that Secondary VM is running. It can also be applied for FT/HA > > Please define COLO and FT/HA on first use (okay to abbreviate elsewhere > in the document, but the first use should not assume the acronym is > well-known) > > s/for COLO that/for COLO (COurse-grain LOck-stepping), where the/ > >> +scene that Secondary VM is not running. > > s/for FT/HA scene that/for the FT/HA (Fault-tolerance/High Assurance) > scenario, where the/ > >> + >> +This document gives an overview of block replication's design. >> + >> +== Background == >> +High availability solutions such as micro checkpoint and COLO will do >> +consecutive checkpoint. The VM state of Primary VM and Secondary VM is > > s/checkpoint/checkpoints/ > >> +identical right after a VM checkpoint, but becomes different as the VM > ... >> + >> +4) The hidden-disk is created automatically. It buffers the original content >> +that is modified by the primary VM. It should also be an empty disk, and >> +the dirver supports bdrv_make_empty(). > > s/dirver/driver/ > >> + >> +== New block driver interface == >> +We add three block driver interfaces to control block replication: >> +a. bdrv_start_replication() >> + Start block replication, called in migration/checkpoint thread. >> + We must call bdrv_start_replication() in secondary QEMU before >> + calling bdrv_start_replication() in primary QEMU. >> +b. bdrv_do_checkpoint() >> + This interface is called after all VM state is transfered to > > s/transfered/transferred/ > >> + Secondary QEMU. The Disk buffer will be dropped in this interface. >> + The caller must hold the I/O mutex lock if it is in migration/checkpoint >> + thread. >> +c. bdrv_stop_replication() >> + It is called when failover. We will flush the Disk buffer into > > s/when/on/ > >> + Secondary Disk and stop block replication. The vm should be stopped >> + before calling it. The caller must hold the I/O mutex lock if it is >> + in migration/checkpoint thread. >> + >> +== Usage == >> +Primary: >> + -drive if=xxx,driver=quorum,read-pattern=fifo,\ >> + children.0.file.filename=1.raw,\ >> + children.0.driver=raw,\ >> + children.1.file.driver=nbd+colo,\ >> + children.1.file.host=xxx,\ >> + children.1.file.port=xxx,\ >> + children.1.file.export=xxx,\ >> + children.1.driver=raw,\ >> + children.1.ignore-errors=on > > This command line looks like multiple arguments because of the leading > whitespace on succeeding lines. I don't know if there is any better way > to format it, though, to make it obvious that it is all a single > argument to -drive. > >> + Note: >> + 1. NBD Client should not be the first child of quorum. >> + 2. There should be only one NBD Client. >> + 3. host is the secondary physical machine's hostname or IP >> + 4. Each disk must have its own export name. > > Maybe a note 5 to call out the formatting aspect of the command line? > >> + >> +Secondary: >> + -drive if=none,driver=raw,file=1.raw,id=nbd_target1 \ >> + -drive if=xxx,driver=qcow2+colo,file=active_disk.qcow2,export=xxx,\ >> + backing_reference.drive_id=nbd_target1,\ >> + backing_reference.hidden-disk.file.filename=hidden_disk.qcow2,\ >> + backing_reference.hidden-disk.driver=qcow2,\ >> + backing_reference.hidden-disk.allow-write-backing-file=on >> + Then run qmp command: >> +nbd_server_start host:port >> + Note: >> + 1. The export name for the same disk must be the same in primary >> + and secondary QEMU command line >> + 2. The qmp command nbd_server_start mus
Re: [Qemu-block] [RFC PATCH COLO v2 01/13] docs: block replication's description
On 2015/3/26 16:58, Wen Congyang wrote: > On 03/25/2015 11:38 PM, Eric Blake wrote: >> > On 03/25/2015 03:36 AM, Wen Congyang wrote: >>> >> Signed-off-by: Wen Congyang >>> >> Signed-off-by: Paolo Bonzini >>> >> Signed-off-by: Yang Hongyang >>> >> Signed-off-by: zhanghailiang >>> >> Signed-off-by: Gonglei >>> >> --- >>> >> docs/block-replication.txt | 147 >>> >> + >>> >> 1 file changed, 147 insertions(+) >>> >> create mode 100644 docs/block-replication.txt >>> >> >> > >> > Grammar review only (I'll leave the technical review to others) >> > >>> >> diff --git a/docs/block-replication.txt b/docs/block-replication.txt >>> >> new file mode 100644 >>> >> index 000..874ed8e >>> >> --- /dev/null >>> >> +++ b/docs/block-replication.txt >>> >> @@ -0,0 +1,147 @@ >>> >> +Block replication >>> >> + >>> >> +Copyright Fujitsu, Corp. 2015 >>> >> +Copyright (c) 2015 Intel Corporation >>> >> +Copyright (c) 2015 HUAWEI TECHNOLOGIES CO.,LTD. >> > >> > Space after comma in English writing. > Yes, but I am not sure I can change it. HUAWEI always use this way. > You can find it in bootdevice.c Good catch, Eric is right. I will change all of this writing way in Qemu at 2.4. Thanks. Regards, -Gonglei
Re: [Qemu-block] [RFC PATCH COLO v2 01/13] docs: block replication's description
On 03/26/2015 04:28 AM, Gonglei wrote: Grammar review only (I'll leave the technical review to others) >> +Copyright Fujitsu, Corp. 2015 >> +Copyright (c) 2015 Intel Corporation >> +Copyright (c) 2015 HUAWEI TECHNOLOGIES CO.,LTD. Space after comma in English writing. >> Yes, but I am not sure I can change it. HUAWEI always use this way. Copyright lines are one thing that I am reluctant to change if it is not my own line (some companies have policies on how their lines must look, and I'm not in a position to argue the policy as I am not a lawyer). >> You can find it in bootdevice.c Such existing precedence is a strong argument to NOT changing it, at least for a patch author that is not the copyright owner. > > Good catch, Eric is right. I will change all of this writing way in Qemu at > 2.4. So, sounds like such a change would be a separate patch (probably through the -trivial tree), and cover all files in the repo in one go, without affecting this series. Such a patch by a copyright owner would have no problem being accepted, if it is wanted. -- Eric Blake eblake redhat com+1-919-301-3266 Libvirt virtualization library http://libvirt.org signature.asc Description: OpenPGP digital signature
Re: [Qemu-block] [RFC PATCH COLO v2 01/13] docs: block replication's description
On 2015/3/26 20:30, Eric Blake wrote: > On 03/26/2015 04:28 AM, Gonglei wrote: > > Grammar review only (I'll leave the technical review to others) > > >>> +Copyright Fujitsu, Corp. 2015 >>> +Copyright (c) 2015 Intel Corporation >>> +Copyright (c) 2015 HUAWEI TECHNOLOGIES CO.,LTD. > > Space after comma in English writing. >>> Yes, but I am not sure I can change it. HUAWEI always use this way. > > Copyright lines are one thing that I am reluctant to change if it is not > my own line (some companies have policies on how their lines must look, > and I'm not in a position to argue the policy as I am not a lawyer). > >>> You can find it in bootdevice.c > > Such existing precedence is a strong argument to NOT changing it, at > least for a patch author that is not the copyright owner. > >> >> Good catch, Eric is right. I will change all of this writing way in Qemu at >> 2.4. > > So, sounds like such a change would be a separate patch (probably > through the -trivial tree), and cover all files in the repo in one go, > without affecting this series. Such a patch by a copyright owner would > have no problem being accepted, if it is wanted. > Okay, will do, if it is not too later for rc2. :) Thanks, -Gonglei
Re: [Qemu-block] [RFC PATCH COLO v2 01/13] docs: block replication's description
On 03/26/2015 02:31 PM, Fam Zheng wrote: > On Wed, 03/25 17:36, Wen Congyang wrote: >> Signed-off-by: Wen Congyang >> Signed-off-by: Paolo Bonzini >> Signed-off-by: Yang Hongyang >> Signed-off-by: zhanghailiang >> Signed-off-by: Gonglei >> --- >> docs/block-replication.txt | 147 >> + >> 1 file changed, 147 insertions(+) >> create mode 100644 docs/block-replication.txt >> >> diff --git a/docs/block-replication.txt b/docs/block-replication.txt >> new file mode 100644 >> index 000..874ed8e >> --- /dev/null >> +++ b/docs/block-replication.txt >> @@ -0,0 +1,147 @@ >> +Block replication >> + >> +Copyright Fujitsu, Corp. 2015 >> +Copyright (c) 2015 Intel Corporation >> +Copyright (c) 2015 HUAWEI TECHNOLOGIES CO.,LTD. >> + >> +This work is licensed under the terms of the GNU GPL, version 2 or later. >> +See the COPYING file in the top-level directory. >> + >> +The block replication is used for continuous checkpoints. It is designed >> +for COLO that Secondary VM is running. It can also be applied for FT/HA >> +scene that Secondary VM is not running. >> + >> +This document gives an overview of block replication's design. >> + >> +== Background == >> +High availability solutions such as micro checkpoint and COLO will do >> +consecutive checkpoint. The VM state of Primary VM and Secondary VM is >> +identical right after a VM checkpoint, but becomes different as the VM >> +executes till the next checkpoint. To support disk contents checkpoint, >> +the modified disk contents in the Secondary VM must be buffered, and are >> +only dropped at next checkpoint time. To reduce the network transportation >> +effort at the time of checkpoint, the disk modification operations of >> +Primary disk are asynchronously forwarded to the Secondary node. >> + >> +== Workflow == >> +The following is the image of block replication workflow: >> + >> ++--+++ >> +|Primary Write Requests||Secondary Write Requests| >> ++--+++ >> + | | >> + | (4) >> + | V >> + | /-\ >> + | Copy and Forward| | >> + |-(1)--+ | Disk Buffer | >> + | | | | >> + | (3) \-/ >> + | speculative ^ >> + |write through(2) >> + | | | >> + V V | >> + +--+ ++ >> + | Primary Disk | | Secondary Disk | >> + +--+ ++ >> + >> +1) Primary write requests will be copied and forwarded to Secondary >> + QEMU. >> +2) Before Primary write requests are written to Secondary disk, the >> + original sector content will be read from Secondary disk and >> + buffered in the Disk buffer, but it will not overwrite the existing >> + sector content in the Disk buffer. > > Could you elaborate a bit about the "existing sector content" here? IIUC, it > could be from either "Secondary Write Requests" or previous COW of "Primary > Write Requests". Is that right? > >> +3) Primary write requests will be written to Secondary disk. >> +4) Secondary write requests will be buffered in the Disk buffer and it >> + will overwrite the existing sector content in the buffer. >> + >> +== Architecture == >> +We are going to implement COLO block replication from many basic >> +blocks that are already in QEMU. >> + >> + virtio-blk || >> + ^||.-- >> + |||| Secondary >> +1 Quorum ||'-- >> + / \ || >> +/\|| >> + Primary 2 NBD ---> 2 NBD >> + disk client|| server >> virtio-blk >> + ||^ >> ^ >> +. ||| >> | >> +Primary | || Secondary disk <- hidden-disk 4 >> <- active-disk 3 >> +' ||| backing^ >> backing >> + ||| | >> + |||
Re: [Qemu-block] [RFC PATCH COLO v2 01/13] docs: block replication's description
On Fri, 04/03 10:35, Wen Congyang wrote: > On 03/26/2015 02:31 PM, Fam Zheng wrote: > > On Wed, 03/25 17:36, Wen Congyang wrote: > >> Signed-off-by: Wen Congyang > >> Signed-off-by: Paolo Bonzini > >> Signed-off-by: Yang Hongyang > >> Signed-off-by: zhanghailiang > >> Signed-off-by: Gonglei > >> --- > >> docs/block-replication.txt | 147 > >> + > >> 1 file changed, 147 insertions(+) > >> create mode 100644 docs/block-replication.txt > >> > >> diff --git a/docs/block-replication.txt b/docs/block-replication.txt > >> new file mode 100644 > >> index 000..874ed8e > >> --- /dev/null > >> +++ b/docs/block-replication.txt > >> @@ -0,0 +1,147 @@ > >> +Block replication > >> + > >> +Copyright Fujitsu, Corp. 2015 > >> +Copyright (c) 2015 Intel Corporation > >> +Copyright (c) 2015 HUAWEI TECHNOLOGIES CO.,LTD. > >> + > >> +This work is licensed under the terms of the GNU GPL, version 2 or later. > >> +See the COPYING file in the top-level directory. > >> + > >> +The block replication is used for continuous checkpoints. It is designed > >> +for COLO that Secondary VM is running. It can also be applied for FT/HA > >> +scene that Secondary VM is not running. > >> + > >> +This document gives an overview of block replication's design. > >> + > >> +== Background == > >> +High availability solutions such as micro checkpoint and COLO will do > >> +consecutive checkpoint. The VM state of Primary VM and Secondary VM is > >> +identical right after a VM checkpoint, but becomes different as the VM > >> +executes till the next checkpoint. To support disk contents checkpoint, > >> +the modified disk contents in the Secondary VM must be buffered, and are > >> +only dropped at next checkpoint time. To reduce the network transportation > >> +effort at the time of checkpoint, the disk modification operations of > >> +Primary disk are asynchronously forwarded to the Secondary node. > >> + > >> +== Workflow == > >> +The following is the image of block replication workflow: > >> + > >> ++--+++ > >> +|Primary Write Requests||Secondary Write Requests| > >> ++--+++ > >> + | | > >> + | (4) > >> + | V > >> + | /-\ > >> + | Copy and Forward| | > >> + |-(1)--+ | Disk Buffer | > >> + | | | | > >> + | (3) \-/ > >> + | speculative ^ > >> + |write through(2) > >> + | | | > >> + V V | > >> + +--+ ++ > >> + | Primary Disk | | Secondary Disk | > >> + +--+ ++ > >> + > >> +1) Primary write requests will be copied and forwarded to Secondary > >> + QEMU. > >> +2) Before Primary write requests are written to Secondary disk, the > >> + original sector content will be read from Secondary disk and > >> + buffered in the Disk buffer, but it will not overwrite the existing > >> + sector content in the Disk buffer. > > > > Could you elaborate a bit about the "existing sector content" here? IIUC, it > > could be from either "Secondary Write Requests" or previous COW of "Primary > > Write Requests". Is that right? > > > >> +3) Primary write requests will be written to Secondary disk. > >> +4) Secondary write requests will be buffered in the Disk buffer and it > >> + will overwrite the existing sector content in the buffer. > >> + > >> +== Architecture == > >> +We are going to implement COLO block replication from many basic > >> +blocks that are already in QEMU. > >> + > >> + virtio-blk || > >> + ^||.-- > >> + |||| Secondary > >> +1 Quorum ||'-- > >> + / \ || > >> +/\|| > >> + Primary 2 NBD ---> 2 NBD > >> + disk client|| server > >> virtio-blk > >> + ||^ > >>^ > >> +. ||| > >>| > >> +Primary | || Secondary disk <- hid
