Re: Some Performance Advice Needed

"jd(at)commandprompt(dot)com ("Joshua D. Drake")" wrote in pgsql.performance:

> Jeff wrote:
>
>>
>> On Dec 23, 2004, at 9:27 AM, Alex wrote:
>>
>>
>>> Running hdparm reported
>>> A) 920mb/s (SCSI 10k)
>>> B) 270mb/s (SCSI 10k)
>>> C) 1750mb/s (IDE 7.2k)
>>
>>
>>
>> IDE disks lie about write completion (This can be disabled on some
>> drives) whereas SCSI drives wait for the data to actually be written
>> before they report success. It is quite
>> easy to corrupt a PG (Or most any db really) on an IDE drive. Check
>> the archives for more info.
>
> Do we have any real info on this? Specifically which drives? Is SATA the
> same way? What about SATA-II?
> I am not saying it isn't true (I know it is) but this is a blanket
> statement that may or may not be
> true with newer tech.

The name hasn't changed, but don't let that give you the wrong
impression because SCSI continues to improve. I only use SCSI drives in
all my servers, and that's because they always seem to outperform SATA and
IDE when there's a multi-user[1] requirement (of course, the choice of OS
[2] is an important factor here too).

Disk fragmentation also plays a role, but can actually become a
hinderance when in a multi-user environment. I find that the caching
algorithm in the OS that I usually choose [2] actually performs extremely
well when more users are accessing data on volumes where the data is
fragmented. I'm told that this is very similar in the Unix environment as
well. Defragmentation makes more sense in a single-user environment
because there are generally a very small number of files being loaded at
one time, and so a user can benefit hugely from defragmentation.

Here's an interesting article (it comes complete with anonymous non-
logical emotion-based reader comments too):

SCSI vs. IDE: Which is really faster?

http://hardware.devchannel.org/hardwarechannel/03/10/20/1953249.shtml?
tid=20&tid=38&tid=49

[1] A somewhat busy web and/or eMail server certainly counts as a multi-
user requirement. Put a database on it where the data isn't being accessed
sequentially, and that can certainly meet the requirements too.
[2] Nearly all my servers run Novell NetWare.

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