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Re: [Nbd] [PATCH 1/1] NBD: make nbd default to deadline I/O scheduler

Andrew Morton wrote:
On Fri, 8 Feb 2008 09:33:41 -0800 Randy Dunlap <randy.dunlap@...57...> wrote:

On Fri, 08 Feb 2008 11:47:42 -0500 Paul Clements wrote:

There have been numerous reports of problems with nbd and cfq. Deadline gives better performance for nbd, anyway, so let's use it by default.

Please define "problems".  If it's just "slowness" then we can live with
that, but I'd hope that Jens is aware and that it's understood.

It it's "hangs" or "oopses" then we panic.

The two problems I have experienced (which may already be fixed):

1) nbd hangs with cfq on RHEL 5 (2.6.18) -- this may well have been fixed

There's a similar debian bug that has been filed as well:


2) nbd performs about 10% better (the last time I tested) with deadline vs. cfq (the overhead of cfq doesn't provide much advantage to nbd [not being a real disk], and you end up going through the I/O scheduler on the nbd server anyway, so it makes sense that deadline is better with nbd)

There have been posts to nbd-general mailing list about problems with cfq and nbd also.


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