From: Stan Hoeppner <stan@hardwarefreak.com>
To: lilofile <lilofile@aliyun.com>
Cc: linux-raid <linux-raid@vger.kernel.org>
Subject: Re: 答复：答复：two raid5 performance
Date: Mon, 16 Dec 2013 22:37:19 -0600 [thread overview]
Message-ID: <52AFD4FF.4050400@hardwarefreak.com> (raw)
In-Reply-To: <a9545b2f-d9be-4616-be40-59bfff151032@aliyun.com>
On 12/16/2013 7:13 AM, lilofile wrote:
> mpt2sas 6Gb/s, PCIE 2.0，the card is four port,so theoretical ratio can reach to 2.4Gb/s,it is not bottleneck. I test read two raid5 using dd,
> such as dd if=/dev/md0 of=/dev/zero 1M
> dd if=/dev/md1 of=/dev/zero 1M
> the total read bandwidth can reach to 2.3GB/s,so I/O bus is not a problem.
Why are you using dd again? I explained to you in your previous thread
why dd will never saturate your SSDs with write IO. Use FIO. If you
don't know how to make FIO do what you want then ask.
BTW, don't start a new thread for the same issue. Your last thread and
this thread deal with the same RAID5 on STEC SSDs issue. By starting a
new thread everyone loses context and history, which are critically
important when keeping track of performance tests and configurations.
I can't help but point out some irony here. You're concerned with
throughput, yet you're connecting 12 SSDs, ~500 MB/s each, to an SAS
backplane which connects via 4-lane 6G SAS to the HBA. With RAID5
that's 5 GB/s SAS hardware throughput funneled through a 2.4 GB/s
SFF-8088 cable. So once you test properly, and see the write throughput
you already have, you'll see you're limited to half the hardware
throughput by your cabling/backplane. For reads you already are seeing
this limit.
--
Stan
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prev parent reply other threads:[~2013-12-17 4:37 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-16 1:07 two raid5 performance lilofile
2013-12-16 7:52 ` Pieter De Wit
2013-12-16 7:57 ` 答复：two " lilofile
2013-12-16 12:29 ` 答复：答复：two " lilofile
2013-12-16 12:45 ` Tommy Apel
2013-12-16 12:57 ` 答复：答复：答复：two " lilofile
2013-12-16 13:08 ` Tommy Apel
2013-12-16 13:06 ` 答复：two " Dag Nygren
2013-12-16 13:32 ` Tommy Apel
2013-12-16 13:55 ` 答复：答复：two " lilofile
2013-12-16 14:02 ` Tommy Apel
2013-12-16 14:21 ` 答复：答复：答复：two " lilofile
2013-12-16 13:13 ` 答复：答复：two " lilofile
2013-12-16 16:32 ` Jiang, Dave
2013-12-17 4:37 ` Stan Hoeppner [this message]
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