The man page says "strip size", not "chunk size", which is correct?
RAID5:
"strip size" = ("Number of disks in array" - 1) * "chunk size"
RAID6:
"strip size" = ("Number of disks in array" - 2) * "chunk size"
"Number of disks in array" does not include spares!
It would be GREAT for performance if writes were full strips at a time,
since no reads would be required.
I don't think it would help performance if writes were full chunks at a
time, since the target chunk would still need to be read to compute the
parity chunk.
Any filesystem gods out there? Any opinions?
Guy
-----Original Message-----
From: linux-raid-owner@xxxxxxxxxxxxxxx
[mailto:linux-raid-owner@xxxxxxxxxxxxxxx] On Behalf Of John Lange
Sent: Wednesday, May 19, 2004 9:42 PM
To: Guy
Cc: 'LinuxRaid'
Subject: RE: Please review: Slackware RAID How-To
On Sun, 2004-05-16 at 23:51, Guy wrote:
> md2 has 4 disks with a chunk size of 128K. Since only 3 disks are used
for
> data, and the filesystem block size is 4K, the stride size should be
> 128*3/4, or 96.
> Change:
> mke2fs -b 4096 -R stride=32 /dev/md2
> To:
> mke2fs -b 4096 -R stride=96 /dev/md2
>
> My logic:
> "Stripe size" is "chunk size" times "number of data disks".
> From example:
> "chunk size" = 128
> "number of data disks" = "nr-raid-disks" - 1 (-2 if RAID6)
I think this is incorrect. At this point I defer to the
Software-RAID-HOWTO.
http://www.tldp.org/HOWTO/Software-RAID-HOWTO-5.html#ss5.10
>From that document stride is chucksize/blocksize . Number of disks does
not enter into it.
So with a chunksize of 128, and a block size of 4 it would be:
128K/4K = 32 for stride.
If this is indeed correct I will be sure to expand that area of the
How-To so it is more clear.
Thanks very much for your feedback.
Regards,
John Lange
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