[rt-users] Hardware Config

[Matthew Seaman]

Jesse Vincent wrote:
> 
>> I agree completely with the above, but more important to me than just RAM
>> and processing power is the speed of disk access.  He mentioned using RAID
>> 5 in a follow-up post.  That's fine, but are these IDE or 15k SCSI drives?
>> Faster drives should always speed up database performance.
> 
> At 8 gigs of RAM on a well-tuned system, most of what RT is pulling out 
> of the database should always be cached in memory.  If MySQL is going to
> disk on every query, the game's over and you're better off sobbing
> quietly into a stiff drink than getting faster disks.

Well, yeah.  Bump up your query_cache_size and that will be true for frequently
run SELECTs.  Bump up tmp_table_size / max_heap_query_size while you're about it
so sorts are all done in RAM as well.  (RT seems to generate quite a lot of
sorting...)

However, databases having this thing about committing changes to persistent storage
means that they are always going to be doing disk IO, and slow disks are going
to hurt performance on INSERT, UPDATE, DELETE or anything else that modifies
data or schema.  And that's going to delay any subsequent SELECTs that can't be
satisfied out of the query cache.

On RAID5 -- unless you've got a really, really expensive RAID controller card, 
RAID5 is always going to be sub-optimal for the sort of small, randomized IOs
that databases generate.  Of course, if you can afford a good enough RAID
controller that it makes RAID5 fast enough, you can almost certainly afford a
few extra disks and use RAID10 instead, and it will be even faster...  

	Cheers,

	Matthew

-- 
Dr Matthew Seaman                     The Bunker, Ash Radar Station
PGP: 0x60AE908C on servers            Marshborough Rd
Tel: +44 1304 814890                  Sandwich
Fax: +44 1304 814899                  Kent, CT13 0PL, UK

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