Re: Write-intent bitmap decreases or increase performance of RAID5?

flag: direct use direct I/O for data
can be useful too

On Wed, Jun 30, 2010 at 12:23 PM, Roman Mamedov [off-list ref] wrote:

On Wed, 30 Jun 2010 08:58:28 +0200 (CEST)
Mikael Abrahamsson [off-list ref] wrote:

quoted

On Wed, 30 Jun 2010, Roman Mamedov wrote:

quoted

This is not necessary. See the dd man page about the conv=fdatasync switch.
You can even test with just 256 MB this way, and still get an extremely
accurate result.

You're right, for writing this is ok. For read tests it's important to use
more than ram though, to avoid doing performance testing from block cache
instead of from the actual drives.

Yeah, though there's also an alternative way of mitigating the effect of
the cache when testing read speed, see http://linux-mm.org/Drop_Caches

--
With respect,
Roman

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Best regards,
[COOLCOLD-RIPN]