Message-ID: <44564C3F.2040609@aviawest.com>
Date: Mon, 01 May 2006 10:58:23 -0700
From: Erik Myllymaki <erik.myllymaki@aviawest.com>
Reply-To: erik.myllymaki@aviawest.com
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To: Mark Lewis <mark.lewis@mir3.com>
Cc: Vivek Khera <vivek@khera.org>,
	Pgsql performance <pgsql-performance@postgresql.org>
Subject: Re: hardare config question
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	<3DFCE70E-E4BB-40AB-B27F-99E90E8159CA@khera.org>
	<1146246441.15712.41.camel@archimedes>
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I have been in discussion with 3ware support and after adjusting some settings, 
the 3ware card in RAID 1 gets better performance than the single drive. I guess 
this had everything to do with the write (and maybe read?) cache.

Of course now i am in a dangerous situation - using volatile write cache 
without a BBU.

If I were to use a UPS to ensure a soft shutdown in the event of power loss, am 
I somewhat as safe as if I were to purchase a BBU for this RAID card?


Thanks.

Mark Lewis wrote:
> It's also possible that the single SATA drive you were testing (or the
> controller it was attached to) is lying about fsync and performing write
> caching behind your back, whereas your new controller and drives are
> not.
> 
> You'll find a lot more info on the archives of this list about it, but
> basically if your application is committing a whole lot of small
> transactions, then it will run fast (but not safely) on a drive which
> lies about fsync, but slower on a better disk subsystem which doesn't
> lie about fsync.
> 
> Try running a test with fsync=off with your new equipment and if it
> suddenly starts running faster, then you know that's the problem.
> You'll either have a choice of losing all of your data the next time the
> system shuts down uncleanly but being fast, or of running slow, or of
> fixing the applications to use chunkier transactions.
> 
> -- Mark
> 
> On Fri, 2006-04-28 at 13:36 -0400, Vivek Khera wrote:
>> On Apr 28, 2006, at 11:37 AM, Erik Myllymaki wrote:
>>
>>> When I had this installed on a single SATA drive running from the  
>>> PE1800's on-board SATA interface, this operation took anywhere from  
>>> 65-80 seconds.
>>>
>>> With my new RAID card and drives, this operation took 272 seconds!?
>> switch it to RAID10 and re-try your experiment.  if that is fast,  
>> then you know your raid controller does bad RAID5.
>>
>> anyhow, I have in one server (our office mail server and part-time  
>> development testing box) an adaptec SATA RAID from dell.  it is  
>> configured for RAID5 and does well for normal office stuff, but when  
>> we do postgres tests on it, it just is plain old awful.
>>
>> but I have some LSI based cards on which RAID5 is plenty fast and  
>> suitable for the DB, but those are SCSI.
>>
>> For what it is worth, the Dell PE1850 internal PERC4/Si card is  
>> wicked fast when hooked up with a pair of U320 SCSI drives.
>>
>>
>>
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