* What is the sector size in /sys/block/md*/md items?
@ 2014-02-22 1:11 Eyal Lebedinsky
2014-02-24 2:29 ` NeilBrown
0 siblings, 1 reply; 2+ messages in thread
From: Eyal Lebedinsky @ 2014-02-22 1:11 UTC (permalink / raw)
To: list linux-raid
I am reading the kernel Documentation/md.txt.
It explains what md the items in sysfs mean. It refers a few times to "sectors".
- Are we talking 512 bytes or the underlying physical disk sector size?
- Do all disks in an array need to have the same sector size?
Seeing how md can be built over physical disks, partitions, loop mounts and more,
I expect that 'sector' is short for '512 bytes' and real disk sector size is not
relevant here.
Nevertheless, there is md*/queue/hw_sector_size which gives 512. So there are now
a few sector sizes (the array and the underlying devices) and the text does not
make it clear which is used where. I assume the array cluster size is the one
referred to in this document.
TIA
--
Eyal Lebedinsky (eyal@eyal.emu.id.au)
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: What is the sector size in /sys/block/md*/md items?
2014-02-22 1:11 What is the sector size in /sys/block/md*/md items? Eyal Lebedinsky
@ 2014-02-24 2:29 ` NeilBrown
0 siblings, 0 replies; 2+ messages in thread
From: NeilBrown @ 2014-02-24 2:29 UTC (permalink / raw)
To: Eyal Lebedinsky; +Cc: list linux-raid
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On Sat, 22 Feb 2014 12:11:58 +1100 Eyal Lebedinsky <eyal@eyal.emu.id.au>
wrote:
> I am reading the kernel Documentation/md.txt.
>
> It explains what md the items in sysfs mean. It refers a few times to "sectors".
> - Are we talking 512 bytes or the underlying physical disk sector size?
Always 512 bytes.
> - Do all disks in an array need to have the same sector size?
No.
>
> Seeing how md can be built over physical disks, partitions, loop mounts and more,
> I expect that 'sector' is short for '512 bytes' and real disk sector size is not
> relevant here.
Correct.
>
> Nevertheless, there is md*/queue/hw_sector_size which gives 512. So there are now
> a few sector sizes (the array and the underlying devices) and the text does not
> make it clear which is used where. I assume the array cluster size is the one
> referred to in this document.
I was never happy when 'queue' appeared under md*. It is almost entirely
irrelevant.
Feel free to post a patch to clarify md.txt.
Thanks,
NeilBrown
>
> TIA
>
> --
> Eyal Lebedinsky (eyal@eyal.emu.id.au)
> --
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