From: Evgeny Shishkin <itparanoia@gmail.com>
To: Craig Ringer <craig@2ndQuadrant.com>
Cc: Niels Kristian Schjødt <nielskristian@autouncle.com>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Do I have a hardware or a software problem?
Date: Wed, 12 Dec 2012 05:17:14 +0400
Message-ID: <2BCB6843-1396-42C9-A5BF-21C7C978FF4B@gmail.com> (raw)
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On Dec 12, 2012, at 5:03 AM, Craig Ringer <craig@2ndQuadrant.com> wrote:
> On 12/12/2012 06:44 AM, Evgeny Shishkin wrote:
>>
>> On Dec 12, 2012, at 2:41 AM, Niels Kristian Schjødt <nielskristian@autouncle.com> wrote:
>>
>>> Are you using a hardware based raid controller with them?
>>>
>> Yes, of course. Hardware raid with cache and bbu is a must. You can't get fast fsync without it.
>
> Most SSDs should offer fairly fast fsync without a hardware RAID controller, as they do write-back caching. The trick is to find ones that do write-back caching safely, so you don't get severe data corruption on power-loss.
>
Actually most of low-end SSDs don't do write caching, they do not have enough ram for that. Sandforce for example.
> A HW RAID controller is an absolute must for rotating magnetic media, though.
>
>> Also mdadm is a pain in the ass and is suitable only on amazon and other cloud shit.
>
> I've personally been pretty happy with mdadm. I find the array portability it offers very useful, so I don't need to buy a second RAID controller just in case my main controller dies and I need a compatible one to get the array running again. If you don't need a BBU for safe write-back caching then mdadm has advantages over hardware RAID.
>
If we are talking about dedicated machine for database with ssd drives, why would anybody don't by hardware raid for about 500-700$?
> I'll certainly use mdadm over onboard fakeraid solutions or low-end hardware RAID controllers. I suspect a mid- to high end HW RAID unit will generally win.
>
> --
> Craig Ringer http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Training & Services
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To: pgsql-performance@postgresql.org
Cc: itparanoia@gmail.com, craig@2ndQuadrant.com, nielskristian@autouncle.com, jeff.janes@gmail.com
Subject: Re: Do I have a hardware or a software problem?
In-Reply-To: <2BCB6843-1396-42C9-A5BF-21C7C978FF4B@gmail.com>
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