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Re: RAID question



Hi, the Berkley Raid definitions define RAID 5 as striping with interleved parity.  because of the number of increased writes and read to commit an actual write to disk, this method is normally used with caching in RAM using fast writes as a method to improve performance.  Striping + Mirroring is RAID 0+1, and Mirroring + Striping is RAID 1+0.   If you have a choice use RAID 1+0 even though it requires twice the number of disks and or controllers.   The reference for all of this stuff is  "Configuration and Capacity Planning for Solaris Servers" Chapter 7.    It is required reading even if you are on another hardware platform, because the generic information is invaluable.

James Hartley



Ed Wilts wrote:
On Mon, 2001-12-17 at 23:27, Stephen Liu wrote:

One additional question I expect to ask, in my case, whether it is 
advisable to apply RAID to build the Web Server simultaneously because the
configuration of Apache, PHP, MySQL will keep me quite busy (I did it once
in 2 years ago). Is RAID difficult to set up ? Which RAID, RAID 0+1,
RAID 5, etc. shall be more applicable to my case ?

RAID 0 is striping and is used *only* for performance reasons. If you
don't think you'll need the additional performance, don't use it. You
will lose redundancy in favor of the performance. If either drive
fails, you lose your data.

RAID 1 is mirroring. When you do your initial Red Hat Linux 7.2
install, you can configure this, and it's easy - it's well documented in
the Installation Guide and takes an extra 5 or 10 minutes to set up, and
then it just runs without you having to do anything else. It's what I
run at home.

RAID 5 is striping + mirroring. I recommend that this not be done on
IDE drives unless you've invested in extra controllers. You need at
least 3 drives to make a RAID 5 set.

RAID 0+1 will give you the highest performance at the expense of the
most drives.

For a home system, RAID 1 is no longer out of the reach of the average
PC purchaser. I added 2 40GB ATA100 dri ves on the Promise TX2
controller for about $240. I mirror the first 10GB of data so that
leaves me 70GB of usuable space. That's a lot of disk space for not a
lot of money. A few years ago, this would have been prohibitively
expensive. Naturally, I still do backups of my data (to hard drives,
not tape).



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