it's ok with discard=unmap option (even if the disc is thick-provisioned) : the block used by the test file appears (VM side) or is reset (host side) at zero.
notice that lsblk "thinks" that the disc is a rotational disk (eg. not really SSD) : lsblk -ndo /dev/sda 1 thanks for explanations ! Le mar. 9 avr. 2019 à 20:38, Narcis Garcia <informat...@actiu.net> a écrit : > I see now the simple: > -device virtio-scsi-pci > makes all -disk (media=disk) to be detected by guest as SSD > > Additionally, adding "discard=unmap,detect-zeroes=unmap" to disk image > specification makes host Qemu to discard sparse image holes and recover > host disk space when guest sends discard signal! > > This is my successful test with Debian 9 (stable): > > $ dd if=/dev/zero of=ssd.img obs=1M seek=128 count=0 > $ qemu-system-... -device virtio-scsi-pci -drive > file=ssd.img,media=disk,index=0,discard=unmap,detect-zeroes=unmap > > Thank you everyone. > > > El 9/4/19 a les 19:19, Friedrich Oslage ha escrit: > > 1. You need to set the discard option for the -drive parameter, eg > > -drive if=none,...,format=raw,discard=unmap since the default is still > > to simply ignore discards. > > > > You may also want to set the detect-zeroes option to unmap, to discard > > all-zero blocks instead of actually writing them. > > > > > > 2. The disk image you created is thick-provisioned. How is qemu supposed > > to discard anything in that file? It could turn it into a sparse file or > > overwrite it with zeroes I suppose, but both options are undesirable. > > > > To make use of the discard operation your backing storage has to support > > it. Either by beeing thin-provisioned, like qcow2 or raw sparse files, > > or by actually beeing a ssd/nvme disk. > > > > > > 3. Your testing method is flawed. You are using a journaling filesystem > > to write the data but to read it you access the block device directly . > > Even if the discard operation was working strings(1) would still show > > the hello-world string in the journal. > > > > You could try something like this: > > > > $ echo hello, world > /dev/sda > > $ strings /dev/sda > > $ blkdiscard /dev/sda > > $ strings /dev/sda > > > > > > Regards > > Friedrich > > > > On 4/9/19 4:38 PM, Pascal wrote: > >> the blocks do not seem to be discarded on a raw format disk: the data > >> remains on the disk... > >> > >> on host : > >> > >> dd if=/dev/zero of=/tmp/ssd.disk bs=1M count=128 > >> qemu -drive media=disk,file=linux.disk -device virtio-scsi-pci,id=scsi > >> -device scsi-hd,drive=hd -drive > >> if=none,id=hd,file=/tmp/ssd.disk,format=raw > >> > >> on Linux VM : > >> > >> fdisk /dev/sda > >> # create one partition on gpt type... > >> fdisk -l /dev/sda > >> Disk /dev/sda: 128 MiB, 134217728 bytes, 262144 sectors > >> Units: sectors of 1 * 512 = 512 bytes > >> Sector size (logical/physical): 512 bytes / 512 bytes > >> I/O size (minimum/optimal): 512 bytes / 512 bytes > >> Disklabel type: gpt > >> Disk identifier: B8D98B8E-7790-4043-8F37-D4D8CA218884 > >> Device Start End Sectors Size Type > >> /dev/sda1 2048 262110 260063 127M Linux filesystem > >> mkfs.ext4 -L ssd /dev/sda1 > >> mount /dev/sda1 /ssd > >> mount > >> /dev/sda1 on /ssd type ext4 (rw,relatime,data=ordered) > >> echo hello world > /ssd/test > >> cat /ssd/test > >> hello world > >> sync && sysctl -q vm.drop_caches=3 > >> rm -f /ssd/test > >> sync && sysctl -q vm.drop_caches=3 > >> fstrim /ssd > >> umount /ssd > >> strings /dev/sda1 | grep 'hello world' > >> hello world > >> > >> > >> Le mar. 9 avr. 2019 à 08:36, Narcis Garcia <informat...@actiu.net> a > >> écrit : > >> > >>> Thank you. > >>> > >>> * I use RAW images because of it's easier to offline mount/chroot when > >>> some issue happens. > >>> * I call directly qemu instead of libvirt > >>> > >>> I'll try to parse these parameters to a qemu-system call. > >>> > >>> > >>> El 8/4/19 a les 22:03, Friedrich Oslage ha escrit: > >>>> Yes. > >>>> > >>>> You'll have to use the virtio-scsi driver, to my knowledge it's the > >>>> only > >>>> driver that supports block discards. > >>>> > >>>> Quick example: > >>>> > >>>> # create a new empty disk > >>>> $ qemu-img create -f qcow2 disk.qcow2 10G > >>>> > >>>> # check size, should only be a few kilobytes > >>>> $ du -sh disk.qcow2 > >>>> > >>>> # add it to your vm > >>>> $ virtsh edit your-vm > >>>> <disk type='block' device='disk'> > >>>> <driver name='qemu' type='qcow2' discard='unmap' > >>>> detect_zeroes='unmap'/> > >>>> <source dev='/tmp/disk.qcow2'/> > >>>> <target dev='sda' bus='scsi'/> > >>>> <address type='drive' controller='0' bus='0' target='0' > unit='0'/> > >>>> </disk> > >>>> <controller type='scsi' index='0' model='virtio-scsi'> > >>>> <driver queues='4'/> > >>>> </controller> > >>>> > >>>> # in your vm, format and mount it > >>>> $ mkfs.ext4 /dev/sda > >>>> $ mount /dev/sda /mnt/discardtest > >>>> > >>>> # put some data on it > >>>> $ dd if=/dev/urandom of=/mnt/discardtest/dummy.bin bs=1M count=1000 > >>>> $ sync > >>>> > >>>> # on host, check size...it should be about 1GB > >>>> $ du -sh disk.qcow2 > >>>> > >>>> # in vm, delete file and trim it > >>>> $ rm /mnt/discardtest/dummy.bin > >>>> $ sync > >>>> $ fstrim /mnt/discardtest > >>>> > >>>> # on host, check size...should only be a few megabytes > >>>> $ du -sh disk.qcow2 > >>>> > >>>> > >>>> It works with other guest OSes as well, for Windows you just use the > >>>> Optimize-Volume cmdlets instead of fstrim. > >>>> > >>>> You also don't have to use qcow2 for backing. Anything that can handle > >>>> discards will do, including sparse files. > >>>> > >>>> > >>>> My advice, however, would be to use qcow2, since sparse files don't > >>>> work > >>>> particularly well. Executing the example above would leave you with > >>>> about 300MB at the end instead of less than 10MB. > >>>> > >>>> Regards > >>>> Friedrich > >>>> > >>>> On 4/5/19 4:04 PM, Narcis Garcia wrote: > >>>>> No; I want to study the possibility of recovering allocated blocs of > >>>>> host filesystem when guest filesystem removes its files > >>>>> (unallocates its > >>>>> blocks). > >>>>> Host -> HD or SSD (independent) with sparse-mode image > >>>>> Guest -> Virtual SSD (to signal discards) > >>>>> > >>>>> > >>>>> El 5/4/19 a les 16:01, Pascal ha escrit: > >>>>>> hello, > >>>>>> > >>>>>> if I understand correctly, you want to study the possibility of > >>>>>> recovering deleted files from an SSD disk: is that right ? > >>>>>> > >>>>>> regards, lacsaP. > >>>>>> > >>>>>> Le jeu. 4 avr. 2019 à 08:24, Narcis Garcia <informat...@actiu.net > >>>>>> <mailto:informat...@actiu.net>> a écrit : > >>>>>> > >>>>>> Is there a way to specify a disk to be detected as an SSD > >>>>>> drive? > >>>>>> > >>>>>> Once reached this, I want to look for the possibility to > >>>>>> recover > >>>>>> host > >>>>>> space when a guest discards disk image blocks, and this > >>>>>> image is > >>>>>> RAW > >>>>>> format and sparse allocated file. > >>>>>> > >>>>>> Thank you. > >>>>>> > >>> > > > >
