linux-kernel - Re: Slow disks.

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Date:	Sun, 26 Dec 2010 23:07:45 +0100
From:	Niels <zorglub_olsen@...mail.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: Slow disks.

On Friday 24 December 2010 16:24, Michael Tokarev wrote:

[snip]
> The thing is, for these WD*EARS drivers, it is _vital_ to get
> proper alignment of all partitions and operations.  They've
> 4Kb sectors physically but report 512bytes sectors to the OS.
> It is _essential_ to ensure all partitions are aligned to the
> 4Kb sectors.  Be it LVM, raid-something, etc - each filesystem
> must start at a 4kb boundary at least, or else you'll see
> _dramatic_ write speed problems.
> 
> So.. check the whole storage stack and ensure proper alignment
> everywhere.  In particular, check that your partitions are not
> aligned to 63 sectors (512b), or starts at N+1 sector - the
> most problematic mode for these drives.
[snip]

I have several of these drives, in various sizes. They seem to be aligned to
63 as you mention:

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1              63      208844      104391   83  Linux
/dev/sda2          208845    19759949     9775552+  82  Linux swap / Solaris
/dev/sda3        19759950   215094284    97667167+  83  Linux
/dev/sda4       215094285   781417664   283161690   83  Linux

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1              63  1953520064   976760001   83  Linux


Is that bad?

What can I do to repair it?

What can I do to prevent it from happening again?


Thanks,
Niels




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