From: Scott Carey <scott@richrelevance.com>
To: Scott Marlowe <scott.marlowe@gmail.com>
To: Stef Telford <stef@ummon.com>
Cc: Greg Smith <gsmith@gregsmith.com>
Cc: Mark Kirkwood <markir@paradise.net.nz>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Raid 10 chunksize
Date: Wed, 1 Apr 2009 15:15:36 -0700
Message-ID: <C5F93598.40BF%scott@richrelevance.com> (raw)
In-Reply-To: <dcc563d10904010954u582600a9t721fd1a2050a802f@mail.gmail.com>
On 4/1/09 9:54 AM, "Scott Marlowe" <scott.marlowe@gmail.com> wrote:
> On Wed, Apr 1, 2009 at 10:48 AM, Stef Telford <stef@ummon.com> wrote:
>> Scott Marlowe wrote:
>>> On Wed, Apr 1, 2009 at 10:15 AM, Stef Telford <stef@ummon.com> wrote:
>>>
>>>> I do agree that the benefit is probably from write-caching, but I
>>>> think that this is a 'win' as long as you have a UPS or BBU adaptor,
>>>> and really, in a prod environment, not having a UPS is .. well. Crazy ?
>>>>
>>>
>>> You do know that UPSes can fail, right? En masse sometimes even.
>>>
>> Hello Scott,
>> Well, the only time the UPS has failed in my memory, was during the
>> great Eastern Seaboard power outage of 2003. Lots of fond memories
>> running around Toronto with a gas can looking for oil for generator
>> power. This said though, anything could happen, the co-lo could be taken
>> out by a meteor and then sync on or off makes no difference.
>
> Meteor strike is far less likely than a power surge taking out a UPS.
> I saw a whole data center go black when a power conditioner blew out,
> taking out the other three power conditioners, both industrial UPSes
> and the switch for the diesel generator. And I have friends who have
> seen the same type of thing before as well. The data is the most
> expensive part of any server.
>
Yeah, well I¹ve had a RAID card die, which broke its Battery backed cache.
They¹re all unsafe, technically.
In fact, not only are battery backed caches unsafe, but hard drives. They
can return bad data. So if you want to be really safe:
1: don't use Linux -- you have to use something with full data and metadata
checksums like ZFS or very expensive proprietary file systems.
2: combine it with mirrored SSD's that don't use write cache (so you can
have fsync perf about as good as a battery backed raid card without that
risk).
4: keep a live redundant system with a PITR backup at another site that can
recover in a short period of time.
3: Run in a datacenter well underground with a plutonium nuclear power
supply. Meteor strikes and Nuclear holocaust, beware!
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To: pgsql-performance@postgresql.org
Cc: scott@richrelevance.com, scott.marlowe@gmail.com, stef@ummon.com, gsmith@gregsmith.com, markir@paradise.net.nz
Subject: Re: Raid 10 chunksize
In-Reply-To: <C5F93598.40BF%scott@richrelevance.com>
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