Re: How to improve db performance with $7K?

Well, more like they both are allowed to issue disk
requests and the magical "clustered file system" manages
locking, etc.

In reality, any disk is only reading/writing to one part of
the disk at any given time, of course, but that in the multiple
initiator deal, multiple streams of requests from multiple hosts
can be queued.



-----Original Message-----
From: Bruce Momjian [mailto:pgman@candle.pha.pa.us]
Sent: Tuesday, April 19, 2005 12:16 PM
To: Mohan, Ross
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORM] How to improve db performance with $7K?


Mohan, Ross wrote:
> Clustered file systems is the first/best example that
> comes to mind. Host A and Host B can both request from diskfarm, eg.

So one host writes to part of the disk and another host writes to a different part?

---------------------------------------------------------------------------

> -----Original Message-----
> From: Bruce Momjian [mailto:pgman@candle.pha.pa.us]
> Sent: Tuesday, April 19, 2005 12:10 PM
> To: Mohan, Ross
> Cc: pgsql-performance@postgresql.org
> Subject: Re: [PERFORM] How to improve db performance with $7K?
>
>
> Mohan, Ross wrote:
> > The only part I am pretty sure about is that real-world experience
> > shows SCSI is better for a mixed I/O environment.  Not sure why,
> > exactly, but the command queueing obviously helps, and I am not sure
> > what else does.
> >
> > ||  TCQ is the secret sauce, no doubt. I think NCQ (the SATA version
> > || of per se drive request reordering)
> >    should go a looong way (but not all the way) toward making SATA 'enterprise acceptable'. Multiple
> >    initiators (e.g. more than one host being able to talk to a drive) is a biggie, too. AFAIK only SCSI
> >    drives/controllers do that for now.
>
> What is 'multiple initiators' used for in the real world?
>
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--
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073