Re: New server: SSD/RAID recommendations?

On 7/7/2015 05:56, Mkrtchyan, Tigran wrote:
>
> ----- Original Message -----
>> From: "Graeme B. Bell" <graeme(dot)bell(at)nibio(dot)no>
>> To: "Mkrtchyan, Tigran" <tigran(dot)mkrtchyan(at)desy(dot)de>
>> Cc: "Graeme B. Bell" <graeme(dot)bell(at)nibio(dot)no>, "Steve Crawford" <scrawford(at)pinpointresearch(dot)com>, "Wes Vaske (wvaske)"
>> <wvaske(at)micron(dot)com>, "pgsql-performance" <pgsql-performance(at)postgresql(dot)org>
>> Sent: Tuesday, July 7, 2015 12:38:10 PM
>> Subject: Re: [PERFORM] New server: SSD/RAID recommendations?
>> I am unsure about the performance side but, ZFS is generally very attractive to
>> me.
>>
>> Key advantages:
>>
>> 1) Checksumming and automatic fixing-of-broken-things on every file (not just
>> postgres pages, but your scripts, O/S, program files).
>> 2) Built-in lightweight compression (doesn't help with TOAST tables, in fact
>> may slow them down, but helpful for other things). This may actually be a net
>> negative for pg so maybe turn it off.
>> 3) ZRAID mirroring or ZRAID5/6. If you have trouble persuading someone that it's
>> safe to replace a RAID array with a single drive... you can use a couple of
>> NVMe SSDs with ZFS mirror or zraid, and get the same availability you'd get
>> from a RAID controller. Slightly better, arguably, since they claim to have
>> fixed the raid write-hole problem.
>> 4) filesystem snapshotting
>>
>> Despite the costs of checksumming etc., I suspect ZRAID running on a fast CPU
>> with multiple NVMe drives will outperform quite a lot of the alternatives, with
>> great data integrity guarantees.
Lz4 compression and standard 128kb block size has shown to be materially
faster here than using 8kb blocks and no compression, both with rotating
disks and SSDs.

This is workload dependent in my experience but in the applications we
put Postgres to there is a very material improvement in throughput using
compression and the larger blocksize, which is counter-intuitive and
also opposite the "conventional wisdom."

For best throughput we use mirrored vdev sets.

--
Karl Denninger
karl(at)denninger(dot)net <mailto:karl(at)denninger(dot)net>
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