[CentOS] Understanding VDO vs ZFS

Sun May 3 03:07:10 UTC 2020
Erick Perez - Quadrian Enterprises <eperez at quadrianweb.com>

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 at daku.org> 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
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Erick Perez