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SubjectRe: Slow disks.
Date
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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