Re: Understanding VDO vs ZFS

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On May 3, 2020 8:33:33 AM GMT+03:00, Erick Perez - Quadrian Enterprises <eperez@xxxxxxxxxxxxxxx> wrote:
>sorry corrections:
>For this test I created a 40GB lvm volume group with /dev/sdb and
>/dev/sdc
>then a 40GB LV
>then a 60GB VDO vol (for testing purposes)
>
>vdostats --verbose /dev/mapper/vdoas | grep -B6 'saving percent'
>output from just created vdoas
>
>[root@localhost ~]# vdostats --verbose /dev/mapper/vdoas | grep -B6
>'saving
>percent'
>physical blocks                     : 10483712
>  logical blocks                      : 15728640
>  1K-blocks                           : 41934848
>  1K-blocks used                      : 4212024
>  1K-blocks available                 : 37722824
>  used percent                        : 10
>  saving percent                      : 99
>[root@localhost ~]#
>
>FIRST copy CentOS-7-x86_64-Minimal-2003.iso (1.1G) to vdoas from source
>outside vdo volume
>[root@localhost ~]# vdostats --verbose /dev/mapper/vdoas | grep -B6
>'saving
>percent'
>  1K-blocks used                      : 4721348
>  1K-blocks available                 : 37213500
>  used percent                        : 11
>  saving percent                      : 9
>
>SECOND copy  CentOS-7-x86_64-Minimal-2003.iso (1.1G) to vdoas form
>source
>outside vdo volume
>#cp /root/CentOS-7-x86_64-Minimal-2003.iso
>/mnt/vdomounts/CentOS-7-x86_64-Minimal-2003-version2.iso
>  1K-blocks used                      : 5239012
>  1K-blocks available                 : 36695836
>  used percent                        : 12
>  saving percent                      : 52
>
>THIRD  copy  CentOS-7-x86_64-Minimal-2003.iso (1.1G) to
>vdoas form inside vdo volume to inside vdo volume
>  1K-blocks used                      : 5248060
>  1K-blocks available                 : 36686788
>  used percent                        : 12
>  saving percent                      : 67
>
>Then I did this a total of 9 more times to have 10 ISOs copied. Total
>data
>copied 10.6GB.
>
>
>Do note this:
>When using DF, it will show the VDO size, in my case 60G
>when using vdostats it will show the size of the LV, in my case 40G
>Remeber dedupe AND compression are enabled.
>
>The df -hT output shows the logical space occupied by these iso files
>as
>seen by the filesystem on the VDO volume.
>Since VDO manages a logical to physical block map, df sees logical
>space
>consumed according to the file system that resides on top of the VDO
>volume.
>vdostats --hu is viewing the physical block device as managed by VDO.
>Physically a single .ISO image is residing on the disk, but logically
>the
>file system thinks there are 10 copies, occupying 10.6GB.
>
>So at the end I have 10 .ISOs of 1086 1MB blocks (total 10860 1MB
>blocks)
>that yield these results:
>  1K-blocks used                      : 5248212
>  1K-blocks available                 : 36686636
>  used percent                        : 12
>  saving percent                      : 89
>
>So at the end it is using 5248212 1K blocks minus  4212024  initial
>used 1K
>blocks, gives (5248212 - 4212024) = 1036188 1K blocks / 1024 = about
>1012MB
>total.
>
>Hope this helps understanding where the space goes.
>
>BTW: Testing system is CentOS Linux release 7.8.2003 stock. with only
>"yum
>install vdo kmod-kvdo"
>
>History of commands:
>[root@localhost vdomounts]# history
>    2  pvcreate /dev/sdb
>    3  pvcreate /dev/sdc
>    8  vgcreate -v -A y vgvol01 /dev/sdb /dev/sdc
>    9  vgdisplay
>   13  lvcreate -l 100%FREE -n lvvdo01 vgvol01
>   14   yum install vdo kmod-kvdo
>   18  vdo create --name=vdoas --device=/dev/vgvol01/lvvdo01
>--vdoLogicalSize=60G --writePolicy=async
>   19  mkfs.xfs -K /dev/mapper/vdoas
>   20  ls /mnt
>   21  mkdir /mnt/vdomounts
>   22  mount /dev/mapper/vdoas /mnt//vdomounts/
>   26  vdostats --verbose /dev/mapper/vdoas | grep -B6 'saving percent'
>   28  cp /root/CentOS-7-x86_64-Minimal-2003.iso /mnt/vdomounts/ -vvv
>   29  vdostats --verbose /dev/mapper/vdoas | grep -B6 'saving percent'
>   30  cp /root/CentOS-7-x86_64-Minimal-2003.iso
>/mnt/vdomounts/CentOS-7-x86_64-Minimal-2003-version2.iso
>   31  vdostats --verbose /dev/mapper/vdoas | grep -B6 'saving percent'
>   33  cd /mnt/vdomounts/
>   35  cp CentOS-7-x86_64-Minimal-2003-version2.iso
>./CentOS-7-x86_64-Minimal-2003-version3.iso
>   36  vdostats --verbose /dev/mapper/vdoas | grep -B6 'saving percent'
>   37  df
>   39  vdostats --hu
>   40  ls -l --block-size=1MB /root/CentOS-7-x86_64-Minimal-2003.iso
>   41  df -hT
>   42  vdo status | grep Dedupl
>   43  vdostats --hu
>   44  vdostats
>   48  cp CentOS-7-x86_64-Minimal-2003-version2.iso
>./CentOS-7-x86_64-Minimal-2003-version4.iso
>   49  cp CentOS-7-x86_64-Minimal-2003-version2.iso
>./CentOS-7-x86_64-Minimal-2003-version5.iso
>   50  cp CentOS-7-x86_64-Minimal-2003-version2.iso
>./CentOS-7-x86_64-Minimal-2003-version6.iso
>   51  cp CentOS-7-x86_64-Minimal-2003-version2.iso
>./CentOS-7-x86_64-Minimal-2003-version7.iso
>   52  cp CentOS-7-x86_64-Minimal-2003-version2.iso
>./CentOS-7-x86_64-Minimal-2003-version8.iso
>   53  cp CentOS-7-x86_64-Minimal-2003-version2.iso
>./CentOS-7-x86_64-Minimal-2003-version9.iso
>   54  df -hT
>   55  ls -l --block-size=1MB
>   56  vdostats --hu
>   57  df -hT
>   58  df
>   59  vdostats --hu
>   60  vdostats
>   61  vdostats --verbose /dev/mapper/vdoas | grep -B6 'saving percent'
>   62  cat /etc/centos-release
>   63  history
>[root@localhost vdomounts]#
>
>
>
>
>
>On Sat, May 2, 2020 at 10:07 PM Erick Perez - Quadrian Enterprises <
>eperez@xxxxxxxxxxxxxxx> wrote:
>
>> My two cents:
>> 1- Do you have an encrypted filesystem on top of VDO? If yes, you
>will see
>> no benefit from dedupe.
>> 2- can you post the stats of  vdostats –verbose /dev/mapper/xxxxx
>(replace
>> with your device)
>>
>> you can do something like:  "vdostats -verbose /dev/mapper/xxxxxxxx |
>grep
>> -B6 'save percentage'
>>
>>
>>
>>
>> On Sat, May 2, 2020 at 9:54 PM david <david@xxxxxxxx> wrote:
>>
>>> Folks
>>>
>>> I'm looking for a solution for backups because ZFS has failed on me
>>> too many times.  In my environment, I have a large amount of data
>>> (around 2tb) that I periodically back up.  I keep the last 5
>>> "snapshots".  I use rsync so that when I overwrite the oldest
>backup,
>>> most of the data is already there and the backup completes quickly,
>>> because only a small number of files have actually changed.
>>>
>>> Because of this low change rate, I have used ZFS with its
>>> deduplication feature to store the data.  I started using a Centos-6
>>> installation, and upgraded years ago to Centos7.  Centos 8 is on my
>>> agenda.  However, I've had several data-loss events with ZFS where
>>> because of a combination of errors and/or mistakes, the entire store
>>> was lost.  I've also noticed that ZFS is maintained separately from
>>> Centos.  At this moment, the Centos 8 update causes ZFS to
>>> fail.  Looking for an alternate, I'm trying VDO.
>>>
>>> In the VDO installation, I created a logical volume containing two
>>> hard-drives, and defined VDO on top of that logical volume.  It
>>> appears to be running, yet I find the deduplication numbers don't
>>> pass the smell test.  I would expect that if the logical volume
>>> contains three copies of essentially identical data, I should see
>>> deduplication numbers close to 3.00, but instead I'm seeing numbers
>>> like 1.15.  I compute the compression number as follows:
>>>   Use df and extract the value for "1k blocks used" from the third
>column
>>>   use vdostats --verbose and extract the number titled "1K-blocks
>used"
>>>
>>> Divide the first by the second.
>>>
>>> Can you provide any advice on my use of ZFS or VDO without telling
>me
>>> that I should be doing backups differently?
>>>
>>> Thanks
>>>
>>> David
>>>
>>> _______________________________________________
>>> CentOS mailing list
>>> CentOS@xxxxxxxxxx
>>> https://lists.centos.org/mailman/listinfo/centos
>>>
>>
>>
>> --
>>
>> ---------------------
>> Erick Perez
>>
>>
>
>-- 
>
>---------------------
>Erick Perez
>Quadrian Enterprises S.A. - Panama, Republica de Panama
>Skype chat: eaperezh
>WhatsApp IM: +507-6675-5083
>---------------------
>_______________________________________________
>CentOS mailing list
>CentOS@xxxxxxxxxx
>https://lists.centos.org/mailman/listinfo/centos

Hi Erick,

In the end how much space is used as per vdostats ?
Keep in mind that VDO keeps one slab for itself (default is 2GB) and also some metadata is written : https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/storage_administration_guide/vdo-qs-requirements#vdo-ig-storage-reqts

Best Regards,
Strahil Nikolov
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