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Re: Questions on RAID alignment

To: Spelic <spelic@xxxxxxxxxxxxx>
Subject: Re: Questions on RAID alignment
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Fri, 21 Sep 2012 08:38:52 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <505AF9EA.7030603@xxxxxxxxxxxxx>
References: <505AF9EA.7030603@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Sep 20, 2012 at 01:11:38PM +0200, Spelic wrote:
> Hello list
> a few questions
> 1- Does XFS support alignment to concatenation RAIDs (e.g. linear
> over raid1) similarly to striped ones?

No. It's being considered and I know how to do it, but it's lower
priority than other stuff I'm working on at the moment. 

> I am guessing probably su and
> sw should not be specified and the agcount should be multiple of the
> number of the concatenated devices, is that correct?

If you are concatenating RAID0/5/6, then you shoul duse su/sw as per
the alignment of the volumes being concatenated.

> 2- Can mkfs parameters be altered after creation, e.g. after growing
> a RAID and then growing the XFS fs, can I also alter su, sw, agcount
> somehow?

You can alter su/sw as a mount option if the filesystem was made
with them initially.

> 3- I seem to remember there was an xattr that one could attach to
> /home (if /home was under XFS) so that every user (subdir of /home)
> would get a different AG in a different RAID device. I cannot find
> that information anymore on the internet; could you refresh my mind?

Nothing of the sort. if you are using the inode64 allocator, then
each new directory is placed i a different AG. That's as good as it
gets right now.


Dave Chinner

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