On Thursday 01 August 2002 20:05, you wrote:
> > 1) What are you _actually_ going to use it for, and why RAID 5?
>
> It was for a postgres database, but I though about designing a
Then believe me, you want to use RAID10. If you have _serious_ multi-user
application then SCSI disks for transaction log files etc are worthwhile.
Too many of the IDE disks are set up to lie on benchmarks, though the Linux
kernel, tries very hard now (thanks to work on new file systems) to make sure
data really is on disk, when it says it is.
> > RAID 5 has performance drawbacks for some applications eg) one using
> > Random writes.
>
> That's quite true, you can reduce this by using a lot of write caching,
> but i the power goes your.....well don't ask.
Good RAID controllers have battery backed NVRAM for this very reason. But
they don't help the problem with RAID 5 stripes. Imagine you do a random
write on one block in a stripe, and have to recalculate the parity block.
Now work out what other blocks you need to do that, and you will see why
write caching does not help!
This is the last time I'll say it, for DB use RAID 10 not RAID 5!!!
> Yeah, but I like to experiment, shame business don't, they have too much
> to loose I guess, they want something that just works, they don't care ,
Build your own then, you'll enjoy it.
> as long as it's cheap and does the job, probably why so many are still
> using dos based packages to run thier companies. ho hum.
Yes and no. Actually it's more economic reasons, and passing the buck on the
hardware testing. Usually time constraints mean you cannot afford to play
about matching components in a PC that may or may not play well together.
> SCSI is dead , long live the SCSI....
SCSI is great, but fewer and fewer applications really need it, and IDE disk
arrays are eating into the remaining areas. They use IDE connect on disks in
the array, giving each one a channel to itself, and use SCSI interface to
connect to the RAID controller (in array or in PC). Still though a SCSI disk
array with SCART disks is great from maintenance point of view.
Rob
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