From: Shaun Thomas <sthomas@optionshouse.com>
To: David Boreham <david_list@boreham.org>
Cc: pgsql-performance@postgresql.org
Subject: Re: Reliability with RAID 10 SSD and Streaming Replication
Date: Wed, 22 May 2013 13:45:06 -0500
Message-ID: <519D1232.4090701@optionshouse.com> (raw)
In-Reply-To: <519D0107.4000600@boreham.org>
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On 05/22/2013 12:31 PM, David Boreham wrote:
>> Device: r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util
>> sdd 2702.80 19.40 19.67 0.16 14.91 273.68 71.74 0.37 100.00
>> sdd 2707.60 13.00 19.53 0.10 14.78 276.61 90.34 0.37 100.00
>>
>> That's an Intel 710 being crushed by a random read database server
>> workload, unable to deliver even 3000 IOPS / 20MB/s. I have hours of
>> data like this from several servers.
>
> This is interesting. Do you know what it is about the workload that
> leads to the unusually low rps ?
That read rate and that throughput suggest 8k reads. The queue size is
270+, which is pretty high for a single device, even when it's an SSD.
Some SSDs seem to break down on queue sizes over 4, and 15 sectors
spread across a read queue of 270 is pretty hash. The drive tested here
basically fell over on servicing a huge diverse read queue, which
suggests a firmware issue.
Often this is because the device was optimized for sequential reads and
post lower IOPS than is theoretically possible so they can advertise
higher numbers alongside consumer-grade disks. They're Greg's disks
though. :)
--
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604
312-676-8870
sthomas@optionshouse.com
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To: pgsql-performance@postgresql.org
Cc: sthomas@optionshouse.com, david_list@boreham.org
Subject: Re: Reliability with RAID 10 SSD and Streaming Replication
In-Reply-To: <519D1232.4090701@optionshouse.com>
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