[linux-lvm] Need inputs: Performance issues with LVM snapshots

[linux-lvm] Need inputs: Performance issues with LVM snapshots

[Gaikwad, Hemant]

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Hi,
We have been looking at LVM as an option for long term backup using the LVM snapshots. After looking at the various forums and also looking at a few LVM defects, realized that LVM could be a very good option for short term backup, but might result in performance issues if the snapshots are retained for a long time. Also read we should restrict the number of snapshots. We are thinking of keeping it to 3, but do you think that could also be a performance bottleneck. A few forum posts also suggest memory issues with using LVM snapshots. Can you please help with some data on that too. Thanks in advance for making our decision easier. Thanks

Regards,
Hemant Gaikwad


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Re: [linux-lvm] Need inputs: Performance issues with LVM snapshots

[Gionatan Danti]

Il 2022-03-07 12:09 Gaikwad, Hemant ha scritto:
> Hi,
> 
> We have been looking at LVM as an option for long term backup using
> the LVM snapshots. After looking at the various forums and also
> looking at a few LVM defects, realized that LVM could be a very good
> option for short term backup, but might result in performance issues
> if the snapshots are retained for a long time. Also read we should
> restrict the number of snapshots. We are thinking of keeping it to 3,
> but do you think that could also be a performance bottleneck. A few
> forum posts also suggest memory issues with using LVM snapshots. Can
> you please help with some data on that too. Thanks in advance for
> making our decision easier. Thanks
> 
> Regards,

Classical, non-thin LVM snapshots are only meant to be short-lived (just 
enough to take a backup), and the performance penalty you talk about 
does apply.
Thin LVM snapshots, on the other side, command a much lower performance 
penalty and can be long-lived (ie: think about a rolling snapshot 
system).
So if you need multiple, long-lived snapshots, I strongly suggest you to 
check lvmthin.
Regards.

-- 
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8

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Re: [linux-lvm] Need inputs: Performance issues with LVM snapshots

[Demi Marie Obenour]

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On 3/7/22 09:44, Gionatan Danti wrote:
> Il 2022-03-07 12:09 Gaikwad, Hemant ha scritto:
>> Hi,
>>
>> We have been looking at LVM as an option for long term backup using
>> the LVM snapshots. After looking at the various forums and also
>> looking at a few LVM defects, realized that LVM could be a very good
>> option for short term backup, but might result in performance issues
>> if the snapshots are retained for a long time. Also read we should
>> restrict the number of snapshots. We are thinking of keeping it to 3,
>> but do you think that could also be a performance bottleneck. A few
>> forum posts also suggest memory issues with using LVM snapshots. Can
>> you please help with some data on that too. Thanks in advance for
>> making our decision easier. Thanks
>>
>> Regards,
> 
> Classical, non-thin LVM snapshots are only meant to be short-lived (just 
> enough to take a backup), and the performance penalty you talk about 
> does apply.
> Thin LVM snapshots, on the other side, command a much lower performance 
> penalty and can be long-lived (ie: think about a rolling snapshot 
> system).
> So if you need multiple, long-lived snapshots, I strongly suggest you to 
> check lvmthin.
> Regards.

Also worth noting that there is a minimum time to perform an LVM
operation of any type, a bit over 0.2 seconds on my machine.  If you
need to create snapshots exceedingly quickly, then LVM itself will be a
bottleneck.  Virtually all applications will not run into this problem,
however.  The only ones I can think of that will are container or VM
managers that need to spin up a lot of containers or VMs, as Qubes
OS does.  The time I mentioned is the time needed to run the entire LVM
command; the time I/O is suspended for is far, *far* shorter.

-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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