Re: [Qemu-discuss] Discard disk image holes for sparse shrink

[Pascal]

lsblk -ndo ROTA /dev/sda

sorry for the bad copy.

Le mer. 10 avr. 2019 à 12:52, Narcis Garcia <address@hidden> a
écrit :

> Can be this rotational detection be affecting in this case?
>
> https://lists.openvz.org/pipermail/users/2019-April/007564.html
> (Devuan 1.0 VM with distro kernel succeeds with lsblk and fstrim)
>
> How can I make guest OS to detect device as no rotational or true SSD?
>
>
> El 10/4/19 a les 12:47, Narcis Garcia ha escrit:
> > Pascal, I don't understand syntax you use for lsblk.
> > I see this with:
> > $ cat /sys/block/sda/queue/rotational
> >
> >
> > El 10/4/19 a les 12:38, Pascal ha escrit:
> >> 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 <address@hidden> 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 <address@hidden> 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 <
> address@hidden
> >>>>>>>>> <mailto:address@hidden>> 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.
> >>>>>>>>>
> >>>>>>
> >>>>
> >>>
> >>>
> >
>
>