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Re: [ADMIN] H/W RAID 5 on slower disks versus no raid on faster HDDs

From: "Rajesh Kumar Mallah(dot)" <mallah(at)trade-india(dot)com>
To: Steve Crawford <scrawford(at)pinpointresearch(dot)com>,pgsql-performance(at)postgresql(dot)org
Subject: Re: [ADMIN] H/W RAID 5 on slower disks versus no raid on faster HDDs
Date: 2002-11-21 19:08:43
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Lists: pgsql-adminpgsql-performance

Thanks Steve,

recently i have come to know that i can only get 3*18 GB ultra160 10K

my OS is lunux , other parameters are
RAM:2GB , CPU:2*2Ghz Xeon,

i feel i will do away with raid use one disk for the OS 
and pg_dumps

, one for tables and last one for WAL , does this sound good?


On Friday 22 November 2002 00:26, Steve Crawford wrote:
> I had long labored under the impression that RAID 5 should give me better
> performance but I have since encountered many reports that this is not the
> case. Do some searching on Google and you will probably find numerous
> articles.
> Note 3x18 w/RAID5 will give 36GB usable while 2x36 w/o RAID is 72GB.
> You could use mirroring on the 2x36 and have the same usable space.
> A mirrored 2x36 setup will probably yield a marginal hit on writes (vs a
> single disk) and an improvement on reads due to having two drives to read
> from and will (based on the Scientific Wild Ass Guess method and knowing
> nothing about your overall system) probably be faster than the RAID5
> configuration while giving you identical usable space and data safety.
> You also may see improvements due to the 15,000RPM drives (of course RPM is
> sort of an arbitrary measure - you really want to know about track access
> times, latency, transfer rate, etc. and RPM is just one influencing factor
> for the above).
> The quality of your RAID cards will also be important (how fast do they
> perform their calculations, how much buffer do they have) as will the
> overall specs of you system. If you have a bottleneck somewhere other than
> your raw disk I/O then you can throw all the money you want at faster
> drives and see no improvement.
> Cheers,
> Steve
> On Thursday 21 November 2002 8:45 am, you wrote:
> > Hi folks,
> >
> > I have two options:
> > 3*18 GB 10,000 RPM Ultra160 Dual Channel SCSI  controller + H/W Raid 5
> > and
> > 2*36 GB 15,000 RPM Ultra320 Dual Channel SCSI and no RAID
> >
> > Does anyone opinions *performance wise*  the pros and cons of above
> > two options.
> >
> > please take in consideration in latter case its higher RPM and better
> > SCSI interface.
> >
> >
> >
> > Regds
> > Mallah.
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Rajesh Kumar Mallah,
Project Manager (Development)
Infocom Network Limited, New Delhi
phone: +91(11)6152172 (221) (L) ,9811255597 (M)

Visit ,
India's Leading B2B eMarketplace.

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