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Re: xfs_growfs / planned resize / performance impact

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: xfs_growfs / planned resize / performance impact
From: Stefan Priebe <s.priebe@xxxxxxxxxxxx>
Date: Sun, 5 Aug 2012 07:46:33 +0200
Cc: "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
In-reply-to: <20120804224336.GS2877@dastard>
References: <5017E426.2040709@xxxxxxxxxxxx> <20120804224336.GS2877@dastard>
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 wrote:
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.

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.

Growing it by two orders of magnitude
what does that mean? (sorry no native speaker)

Thanks!

Stefan
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