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Re: any chance for xfs shrinking?

To: Andrey Korolyov <andrey@xxxxxxx>,Stefan Priebe - Profihost AG <s.priebe@xxxxxxxxxxxx>
Subject: Re: any chance for xfs shrinking?
From: greg.freemyer@xxxxxxxxx
Date: Tue, 12 May 2015 21:27:09 -0400
Cc: Eric Sandeen <sandeen@xxxxxxxxxxx>,"xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
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On May 12, 2015 2:22:16 PM EDT, Andrey Korolyov <andrey@xxxxxxx> wrote:
>On Tue, May 12, 2015 at 3:41 PM, Stefan Priebe - Profihost AG
><s.priebe@xxxxxxxxxxxx> wrote:
>>
>> Am 12.05.2015 um 14:35 schrieb Eric Sandeen:
>>> On 5/12/15 7:01 AM, Stefan Priebe - Profihost AG wrote:
>>>> Hi,
>>>>
>>>> while cloud / vms usage become more and more popular and qemu now
>also
>>>> offers memory hot add and unplug, cpu hot add and unplug, we still
>>>> suffer from a missing xfs shrink.
>>>
>>> Filesystem shrink is a very different scenario than "cloud / vms"
>needs
>>> for hot memory & cpu plugging, IMHO.
>>>
>>>> I would like to continue to use XFS as it is a rock solid base
>since
>>>> around 10 years for us.
>>>>
>>>> But one missing piece in variable ressource usage for us is disk
>>>> shrinking. Is there any chance to get an xfs online shrinking?
>>>
>>> Under what circumstance does your workflow require a filesystem
>shrink?
>>
>> May be special but there are a lot of customers out there who do not
>> manager their ressources. So they've partners and partners of
>partners.
>> It happens quite often that the disk runs out of space and the
>customer
>> does not know what he can do as third parties control the waste of
>> space. So we are in the situation where we need to extent the
>partition
>> so the customer can continue his business. Later when the partner has
>> solved the issue (real world shows mostly 2 days - 3 weeks) the
>customer
>> wants to shrink again as he does not want to pay the space.
>>
>>> Honest question, I'm not challenging you, but I would like to
>understand
>>> what it is about shrink that is so critical it may cause you to stop
>using
>>> XFS.
>>>
>>> One thing about shrink - while i.e. ext4 supports it, the end result
>of
>>> a shrunk filesystem is a scrambled filesystem.  All those heuristics
>that
>>> made the filesystem reasonably performant as it aged get thrown out
>the
>>> window as the fs scavenges for space into which to shrink the
>filesystem...
>>>
>>> That said, another option is to use the dm-thinp target, and
>allocate /
>>> de-allocate storage resources to the underlying block device as
>needed.
>>
>> We do so while using ceph and trim but the customer pays what he can
>> theoretically use and not what he uses in real. Ceph also does not
>> provide a way to show us the real usage of a rbd disk.
>>
>> Greets,
>> Stefan
>>
>
>
>Am I right in a guess that this indirect management issue is a primary
>reason for having online shrinking as a feature? You can use BTRFS at
>it is supporting in-place shrink and achieved enough stability with
>plain use-cases, with enough necessity. Of course having simular thing
>in an XFS would be quite awesome for a general purpose or for a
>visionary case, but the real-world need in such a feature is a bit
>limited, from at least cloud provider` point of view.
>
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