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Re: Using XFS on Raid

To: James Woolliscroft <j_woolliscroft@xxxxxxxxxxx>
Subject: Re: Using XFS on Raid
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 5 Feb 2015 12:02:21 +1100
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <BLU436-SMTP15464F1CAAC1F46E2593ED0FB3B0@xxxxxxx>
References: <BLU436-SMTP15464F1CAAC1F46E2593ED0FB3B0@xxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Feb 05, 2015 at 12:23:53AM +0000, James Woolliscroft wrote:
> Hi,
> 
>  
> 
> I am new to XFS, I have spent a significant time searching for information
> and have not found any documentation relating to the use of XFS over RAID
> with N Drives where the Stripe Unit >256K.

Use the defaults - they do the right thing.

> It appears that XFS on RHEL7 and clones is limited to a maximum Stripe Unit
> of 256KB.

That's not correct. mkfs.xfs prior to v3.2.2 (i.e the latest) throw
a warning about the default log stripe unit not being able to be set
larger than 256k, but it then sets the lsu to a default of 32k and
continues.

The current version (which I think will hit RHEL7.1) omits
the warning and just sets the lsu to 32k - defaults should just do
the right thing and not bother users who are using defaults.

Either version, however, will still result in the data stripe
unit/width is still going to be 1m/2m in your case.

> I also would like to find some information on how to correctly interpret the
> statistics output when formatting a volume with XFS, particularly as the
> process may use other settings which may require further investigation?

They are a reflection of the command line parameters, or if not
specified, the default CLI values. So, read the mkfs.xfs man page as
it explains what everything means.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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