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Re: I/O hang, possibly XFS, possibly general

To: Peter Grandi <pg_mh@xxxxxxxxxx>
Subject: Re: I/O hang, possibly XFS, possibly general
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 8 Jun 2011 15:18:42 +1000
Cc: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <19950.12549.541440.285348@xxxxxxxxxxxxxxxxxx>
References: <BANLkTim_BCiKeqi5gY_gXAcmg7JgrgJCxQ@xxxxxxxxxxxxxx> <BANLkTim978GhfamN=TEFULP5GdfMu02-7w@xxxxxxxxxxxxxx> <19945.24042.711472.158523@xxxxxxxxxxxxxxxxxx> <201106060929.06814@xxxxxx> <19950.12549.541440.285348@xxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Tue, Jun 07, 2011 at 03:09:09PM +0100, Peter Grandi wrote:
> Personally I'd rather have a file system design with space
> reservations (on detecting an append-like access pattern) and
> truncate-on-close than delayed allocation like XFS;

Welcome to the 1990s, Peter. XFS has been doing this for 15 years.
It is an optimisation used by the delayed allocation mechanism,
not a replacement for it. You might have heard the term
"speculative preallocation" before - this is what it does.

FYI, ext3 has a space reservation infrastructure to try to ensure
contiguous allocation occurs without using delayed allocation. It
doesn't work nearly as well as delayed allocation in ext4, btrfs or
XFS...

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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