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Re: XFS peculiar behavior

To: Yannis Klonatos <klonatos@xxxxxxxxxxxx>
Subject: Re: XFS peculiar behavior
From: Andi Kleen <andi@xxxxxxxxxxxxxx>
Date: Wed, 23 Jun 2010 12:24:27 +0200
Cc: xfs@xxxxxxxxxxx
In-reply-to: <4C21B9AF.9010307@xxxxxxxxxxxx> (Yannis Klonatos's message of "Wed, 23 Jun 2010 10:37:19 +0300")
References: <4C21B9AF.9010307@xxxxxxxxxxxx>
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)
Yannis Klonatos <klonatos@xxxxxxxxxxxx> writes:

>         The problem is that i have noticed that XFS may - not all

Why is that a problem?

> times - split a table over a large disk distance. For
> example in one run i have noticed that a file of 13GByte is split over
> a 4,7TByte distance (I calculate this distance
> by subtracting the final block used for the file with the first
> one. The two disk blocks values are acquired using the
> FIBMAP ioctl).

I don't know if it's the only reason, but XFS does a lot of data
structure locking and updates per allocation group, so spreading
to multiple AGs gives better scalability to many CPUs.

Also I suppose it's good to avoid hot spots on the underlying 
device.

-Andi
-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only.

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