[Gluster-devel] [Gluster-users] Fw: Distributed-Disperse Shard Behavior

[Xavi Hernandez]

Hi,

this problem is most likely caused by the XFS speculative preallocation (
https://linux-xfs.oss.sgi.narkive.com/jjjfnyI1/faq-xfs-speculative-preallocation
)

Regards,

Xavi

On Sat, Feb 5, 2022 at 10:19 AM Strahil Nikolov <hunter86_bg at yahoo.com>
wrote:

> It seems quite odd.
> I'm adding the devel list,as it looks like a bug - but it could be a
> feature ;)
>
> Best Regards,
> Strahil Nikolov
>
>
> ----- Препратено съобщение -----
> *От:* Fox <foxxz.net at gmail.com>
> *До:* Gluster Users <gluster-users at gluster.org>
> *Изпратено:* събота, 5 февруари 2022 г., 05:39:36 Гринуич+2
> *Тема:* Re: [Gluster-users] Distributed-Disperse Shard Behavior
>
> I tried setting the shard size to 512MB. It slightly improved the space
> utilization during creation - not quite double space utilization. And I
> didn't run out of space creating a file that occupied 6gb of the 8gb volume
> (and I even tried 7168MB just fine). See attached command line log.
>
> On Fri, Feb 4, 2022 at 6:59 PM Strahil Nikolov <hunter86_bg at yahoo.com>
> wrote:
>
> It sounds like a bug to me.
> In virtualization sharding is quite common (yet, on replica volumes) and I
> have never observed such behavior.
> Can you increase the shard size to 512M and check if the situation is
> better ?
> Also, share the volume info.
>
> Best Regards,
> Strahil Nikolov
>
> On Fri, Feb 4, 2022 at 22:32, Fox
> <foxxz.net at gmail.com> wrote:
> Using gluster v10.1 and creating a Distributed-Dispersed volume with
> sharding enabled.
>
> I create a 2gb file on the volume using the 'dd' tool. The file size shows
> 2gb with 'ls'. However, 'df' shows 4gb of space utilized on the volume.
> After several minutes the volume utilization drops to the 2gb I would
> expect.
>
> This is repeatable for different large file sizes and different
> disperse/redundancy brick configurations.
>
> I've also encountered a situation, as configured above, where I utilize
> close to full disk capacity and am momentarily unable to delete the file.
>
> I have attached a command line log of an example of above using a set of
> test VMs setup in a glusterfs cluster.
>
> Is this initial 2x space utilization anticipated behavior for sharding?
>
> It would mean that I can never create a file bigger than half my volume
> size as I get an I/O error with no space left on disk.
> ________
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