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From: Sebastian Riemer <sebastian.riemer@profitbricks.com>
To: linux-raid@vger.kernel.org
Subject: Reason for md raid 01 blksize limited to 4 KiB?
Date: Mon, 21 May 2012 10:43:51 +0200	[thread overview]
Message-ID: <4FBA0047.5050208@profitbricks.com> (raw)

Hi list,

I'm wondering why stacking raid1 above raid0 limits the block sizes in
the blkio queue to 4 KiB both read and write.

The max_sectors_kb is at 512. So it's not a matter of limits.

Could someone explain, please? Or could someone pinpoint me to the
related location in the source code?

We've thought of using this for replication via InfiniBand/SRP. 4 KiB
chunks are completely inefficient with SRP. We wanted to do this with
DRBD first, but this is also extremely inefficient, because of chunk
sizes in the blkio queue.

I can reproduce the small 4 KiB chunks also in a file copy benchmark
with raid 01 on ram disks.

Cheers,
Sebastian

             reply	other threads:[~2012-05-21  8:43 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-05-21  8:43 Sebastian Riemer [this message]
2012-05-21 23:14 ` Reason for md raid 01 blksize limited to 4 KiB? Stan Hoeppner
2012-05-21 23:28 ` NeilBrown
2012-05-25 12:35   ` Sebastian Riemer
2012-05-28  4:05     ` NeilBrown
2012-05-29  9:30       ` Sebastian Riemer
2012-05-29 10:25         ` NeilBrown
2012-05-30 13:03           ` Sebastian Riemer
2012-05-31  5:42             ` NeilBrown
2012-05-31  6:18               ` Yuanhan Liu
2012-05-31 10:26               ` Sebastian Riemer

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