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Re: With 4 disks should I go for RAID 5 or RAID 10

From: Shane Ambler <pgsql(at)Sheeky(dot)Biz>
To: Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
Cc: Fernando Hevia <fhevia(at)ip-tel(dot)com(dot)ar>, 'pgsql-performance' <pgsql-performance(at)postgresql(dot)org>
Subject: Re: With 4 disks should I go for RAID 5 or RAID 10
Date: 2007-12-27 07:16:38
Message-ID: 47735156.2080403@Sheeky.Biz (view raw or whole thread)
Lists: pgsql-performance
Mark Mielke wrote:
> Shane Ambler wrote:
>> So in a perfect setup (probably 1+0) 4x 300MB/s SATA drives could
>> deliver 1200MB/s of data to RAM, which is also assuming that all 4
>> channels have their own data path to RAM and aren't sharing. 
>> (anyone know how segregated the on board controllers such as these
>> are?)
 >> (do some pci controllers offer better throughput?)
 >> We all know that doesn't happen in the real world ;-) Let's say we
 >> are restricted to 80% - 1000MB/s - and some of that (10%) gets used
 >> by the system - so we end up with 900MB/s delivered off disk to
>> postgres - that would still be more than the perfect rate at which
>> 2x 300MB/s drives can deliver.
> I achieve something closer to +20% - +60% over the theoretical 
> performance of a single disk with my four disk RAID 1+0 partitions.

If a good 4 disk SATA RAID 1+0 can achieve 60% more throughput than a 
single SATA disk, what sort of percentage can be achieved from a good 
SCSI controller with 4 disks in RAID 1+0?

Are we still hitting the bus limits at this point or can a SCSI RAID 
still outperform in raw data throughput?

I would still think that SCSI would still provide the better reliability 
that it always has, but performance wise is it still in front of SATA?


Shane Ambler
pgSQL (at) Sheeky (dot) Biz

Get Sheeky @ http://Sheeky.Biz

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Subject: Re: With 4 disks should I go for RAID 5 or RAID 10
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Subject: Re: More shared buffers causes lower performances

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