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Re: xfs_growfs / planned resize / performance impact

To: xfs@xxxxxxxxxxx
Subject: Re: xfs_growfs / planned resize / performance impact
From: Martin Steigerwald <Martin@xxxxxxxxxxxx>
Date: Sun, 5 Aug 2012 13:06:56 +0200
Cc: Stefan Priebe <s.priebe@xxxxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>
In-reply-to: <C4E0639A-87DE-4D38-8097-9B71D0947ABE@xxxxxxxxxxxx>
References: <5017E426.2040709@xxxxxxxxxxxx> <20120804224336.GS2877@dastard> <C4E0639A-87DE-4D38-8097-9B71D0947ABE@xxxxxxxxxxxx> (sfid-20120805_095300_150817_93C5E635)
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Am Sonntag, 5. August 2012 schrieb Stefan Priebe:
> Am 05.08.2012 um 00:43 schrieb Dave Chinner <david@xxxxxxxxxxxxx>:
> > On Tue, Jul 31, 2012 at 03:56:54PM +0200, Stefan Priebe - Profihost AG 
> >> Hello list,
> >> 
> >> i'm planning to create a couple of VMs with just 30GB of space while
> >> using xfs as the main filesystem.
> >> 
> >> Now i alreay know that some of the VMs will grow up to 250GB while
> >> resizing the block device and using xfs_growfs.
> > 
> > Just use thin provisioning and make it 250GB to begin with. Thin
> > provisioning mades filsystem grow/shrink pretty much redundant....
> But dm thin isn't stable isn't it? Does xfs reallocate used parts of
> the block Device before using new parts? Otherwise deleting and
> recreating files will result in full used space pretty fast.

A periodic fstrim might help if the TRIM/DISCARD is supported in all 
layers. And whether it is is a good question that depends on well where 
your data is stored and what layers in the kernel are involved in storing 
it and the kernel version of course.

> >> Is it a problem if this grow will happen in small portions (30GB =>
> >> 50GB => 75GB => 100GB => ... 300GB)?
> > 
> > Growing a filesystem by an order of magnitude is the limit of what
> > I'd suggest is sane. Growing it by two orders of magnitude
> > (espcially if you start with a 16 AG filesystem because of stripe
> > alignment) is going to cause problems with the number of AGs and
> > the subsequent freespace management scale issue....
> I would start with ag=4 and end up in ag 48 in my tests.

Thats IMHO quite much for upto 500 GiB. But it still depends on what kind 
of storage this is located.

Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA  B82F 991B EAAC A599 84C7

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