From: NeilBrown <neilb@suse.de>
To: Andras Korn <korn@raidlist.elan.rulez.org>
Cc: linux-raid@vger.kernel.org
Subject: Re: write-behind has no measurable effect?
Date: Tue, 15 Feb 2011 09:50:42 +1100 [thread overview]
Message-ID: <20110215095042.51ef7e0a@notabene.brown> (raw)
In-Reply-To: <20110214213817.GG836@hellgate.intra.guy>
On Mon, 14 Feb 2011 22:38:17 +0100 Andras Korn <korn@raidlist.elan.rulez.org>
wrote:
> Hi,
>
> I experimented a bit with write-mostly and write-behind and found that
> write-mostly provides a very significant benefit (see below) but
> write-behind seems to have no effect whatsoever.
The use-case where write-behind can be expected to have an effect is when the
throughput is low enough to be well within the capacity of all devices, but
the latency of the write-behind device is higher than desired.
write-behind will allow that high latency to be hidden (as long as the
throughput limit is not exceeded).
I suspect your tests did not test for low latency in a low-throughput
scenario.
NeilBrown
next prev parent reply other threads:[~2011-02-14 22:50 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-14 21:38 write-behind has no measurable effect? Andras Korn
2011-02-14 22:50 ` NeilBrown [this message]
2011-02-14 22:57 ` Andras Korn
2011-02-14 23:41 ` NeilBrown
2011-02-15 1:00 ` Andras Korn
2011-02-15 1:19 ` John Robinson
2011-02-15 2:19 ` Andras Korn
[not found] ` <AANLkTikFSOePZJXknAt=Tx6+FpdJ4tiSNwpuwuPC3RY=@mail.gmail.com>
2011-02-15 9:10 ` Roberto Spadim
2011-02-15 12:40 ` Andras Korn
2011-02-15 13:26 ` Roberto Spadim
2011-02-15 17:46 ` Roberto Spadim
2011-02-16 12:00 ` Andras Korn
2011-02-16 15:00 ` Roberto Spadim
2011-02-14 22:56 ` Doug Dumitru
2011-02-14 23:03 ` Andras Korn
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