I want to remove snapshots and I found two ways:
qemu-img commit
qemu-img rebase
I found they both can choose where to rebase(merge) the images.
commit can truncate or not on specific image.
rebase won't truncate rebased image.
I found they have something similarity and I don't know what situatio
I put image on the 3xSSD RAID0, and the raw performance of block device is
read:1500MB/s, write:1400MB/s
The bottleneck I thought is the number of backing files.
The more images I divide into, lower the read performance
Write performance looks like bad originally.
>
> All images are on the RAID0(3 SSD).
>> Below is the performance:
>>
>
image numberseq. read(MB/s)seq. write(MB/s)
11480 60
16 1453 36
32 1450 36
64
>
>
> Both values correspond to L2 entries with bit 0 set. However,
> QCOW2_CLUSTER_ZERO_ALLOC is an entry that has a non-zero value in bits 9-55
> (the cluster has an allocated host location, we guarantee that things read
> as zero regardless of whether the host data actually contains zeroes at
>
I test nbd performance when I divide image into multiple backing files.
The image is 512GB, I divide it into 1, 16, 32, 64, and 128 backing files.
Ex: If I divide it into 16 files, each backing file is 512/16=32GB.
If I divide it into 64 files, each backing file is 512/64=8GB and so on.
*Mount c
I have two image A and B, and A is the backing file of B
I write data in address addr in A.
Then create B and set A as backing file of B.
Then I discard the same addr in B.
So the entry of addr in l2 table should be 1( also is
QCOW2_CLUSTER_ZERO_PLAIN)
, right?
But the addr cluster in A will fil
>
>
> *(That's what I said range is different)*
>> Ex: 1st chunk of device will save into image.000
>> 2nd chunk of device will save into image.001
>> Nth chunk of device will save into image.(N-1)
>> ...etc
>>
>> I can see all block device data when I mount image.(N-1) by qemu-nbd cuz
>> the chunk
The function qcow2_get_cluster_type() is in /block/qcow2.h
It will return the flage based on the entry.
There're some flags confused me.
What's difference between QCOW2_CLUSTER_ZERO_ALLOC &
QCOW2_CLUSTER_ZERO_PLAIN
in there?
Can I convert from internap snapshot to external snapshot?
If there's 3 snapshots in one qcow2, can I convert them all to external
snapshots?
In general case, what's difference between internal and external snapshot?
I mean in some user situation.
Ex: If I want to all snapshots in only one qcow2, I should use internal
snapshot.
thx
Sorry, I need to explain what case I want to do
Todo: I want to *backup a block device into qcow2 format image.*
I met a problem which is the *file size limit of filesystem* ex: Max is
16TB for any file in ext4, but the block device maybe 32TB or more.
I figure out one way is to *divide data of d
I split data to 3 chunks and save it in 3 independent backing files like
below:
img.000 <-- img.001 <-- img.002
img.000 is the backing file of img.001 and 001 is the backing file of 002.
img.000 saves the 1st chunk of data and img.001 saves the 2nd chunk of
data, and img.002 saves the 3rd chunk of
>
> In general, we've spent more resources developing external snapshots. So
> if you want the most support and the fastest response on resolving any
> issues that you may encounter, external snapshots are the way to go.
>
>
So internal snapshot is hard to use than external snapshot?
Is that becaus
I have two qcow2 A & B, and A is backing file of B.
Can I convert both A&B to one image and containing data of both?
ex:
one new image will contain data of A and B. When I check it by qemu-img
info, I can see one snapshot in the new image.
thanks
as title, I know there're two snapshots in qemu, but I don't know when to
use them well.
What I know is internal snapshot will save the info of L1 and L2 table in
the end of image but external snapshot won't because external snapshot
create new file to save cow data.
So when to use internal snaps
I have an qcow2 image and I mount it to /dev/nbd then write somethin.
Then I take internal snapshot in the qcow2.
I enter the command qemu-img info qcow2
It shows:
image: qcow2
file format: qcow2
virtual size: 30G
disk size:4M
x
Snapshot list:
ID, TAG, VM SIZE, DATE, VM CLOCK
1, snap1, 0, xxx
Really? How to mount a blk device to /dev/nbdN?
I always find tips to mount from file-like image to /dev/nbdN
2018-08-16 19:46 GMT+08:00 Eric Blake :
> On 08/16/2018 03:22 AM, Daniel P. Berrangé wrote:
>
>> On Thu, Aug 16, 2018 at 09:35:52AM +0800, lampahome wrote:
>>
>>
We all know there's a file size limit 16TB in ext4 and other fs has their
limit,too.
If I create an qcow2 20TB on ext4 and write to it more than 16TB. Data more
than 16TB can't be written to qcow2.
So, is there any better ways to solve this situation?
What I thought is to create new qcow2 called
I have image A & B, and A is backing file of B.
After I mount A to /dev/nbd0 and I write from position 0~999 in nbd0.
Then create B and set A as backing file of B.
I mount B on /dev/nbd1 and I can saw the data from pos:0~999 because A is
B's backing file. That's reasonable.
But I want to disca
There's file size maximum in ext4 and it's 16TB
Can I create qcow2 ex:32TB and write more than 16TB?
thx
I have some questions about qcow2
If I have 2 img A & B, and A is backing file of B.
Is the format(such as L1, L2, ref block...etc) different from A and B?
> No real tutorial other than reading the code and the file format
> specification (it's open source, after all). See:
> block/qcow2*
> doc
As titled
I learn some info about qcow2 and tried to write some data and make it
qualified for qcow2 format.
I do it and mount through qemu-nbd successfully.
But I don't know how taking snapshot and backing file works in programming
way.
Can someone tell me some tutorial to know or code snippet
I tried take snapshots on a demo.qcow2 10 times.
cmd is below:
> qemu-img snapshots -c tag_1 demo.qcow2
when I take snapshots 7 times and console shows:
> mark image as corrupted and preventing from invalid write
and I can't take snapshots anymore then.
Can I avoid this situation or remove th
I thought 2.9.0 is the latest and check to the wrong commit.
Now it supports encryption.
My cmd is:
> qemu-nbd --object secret,id=sec0,file=passwd.txt,format=raw \
> --image-opts
> driver=qcow2,file.filename=demo.qcow2,encrypt.format=luks,encrypt.key-secret=sec0
But it shows error m
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