Re: RAID: Advantage or disaster?

"Connor McDonald" <connor_mcdonald_at_yahoo.com> wrote in message news:<9uott1$b90$1_at_news7.svr.pol.co.uk>...
> Generally mirrors will give read benefits (using round-robin scheduling or
> even bouncing the request at both and seeing which comes back fastest), and
> minimal write penalty since the writes are done in parallel.

Yes, indeed. When using good RAID controller, RAID1 can be a pretty quick.

> But I do disagree with Dusan's assertion that stripes aren't good.

I do not think that stripes are bad. However everything has some trade-offs. If you can afford to place your data on separate disk sets or even using separate controllers, you will get definitely better performance than using one stripe set. So my suggestion is to use more physical places for your data instead of using one RAID5 set, which do this work (separate files on more disks) for you, but without any control.

For example:

2x18GB RAID1 /u01/SID/data/index01.dbf 2x18GB RAID1 /u02/SID/data/app_data01.dbf 2x9GB RAID1 /u02/SID/data/system01.dbf

will be better than

4x18GB RAID1   /u01/SID/data/index01.dbf
               /u01/SID/data/app_data01.dbf
               /u01/SID/data/system01.dbf

because in the first case you know when your datafiles are. With the second place you can be lucky and have all datafiles separate, but maybe they will be placed together and then you can't expect a great performance.
However in the second case you will save two 9GB disks and 2 drive bays.

--
_________________________________________

Dusan Bolek, Ing.
Oracle team leader

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