Software Raid

Warren Togami warren at togami.com
Tue Sep 11 01:16:56 PDT 2001


Linux software RAID works quite well.  The usual RAID levels supported are
0, 1, 0+1 and 5.

0 is for striping speed
1 is for mirroring redundancy
0+1 is for both
5 has striping speed and parity redundancy, but it will be a little slower
due to the parity bit calculation being done by the system's CPU and not a
controller.

DO NOT stripe swap.  Instead create partitions of equal size on more than
one disk, and give each swap partition an equal priority in swap
configuration.  The Linux VM layer will make more optimal use of multiple
swap partitions across different IO devices than a single paritition across
a RAID device.  Also if you use a real RAID controller with onboard cache
consider not putting swap on this device, as that may be a very sub-optimal
use of the RAID cache.

Generally if you want anything more than two disk RAID 0 or 1, you should
invest in a real RAID controller.  (The Promise and HighPoint IDE RAID
controllers often integrated into cheaper motherboards are very poor RAID
controllers.  They have no onboard cache, and they heavily use the CPU.
Software RAID in Linux and Windows 2000 are more optimal.)

The 3Ware IDE RAID controllers are EXCELLENT.  3Ware controllers have
onboard cache, hot-swap and very optimized onboard controller that can
compete with SCSI RAID in many usages.  IDE has severe advantages over SCSI
in performance and capacity per the dollar.

However, if you want pure speed you must go with plain SCSI or fiber
channel.  I have had good experiences with the AMI MegaRAID SCSI RAID
controller in our dual athlon server at AMDMB.com (excellent Linux support).
Brian Chee mentioned a Symbios 160MBps SCSI controller is really good too,
for only about $70 and all the features: onboard cache, hot-swap, audible
alarm, etc.)

Actually... pure speed would be Platypus presistent RAM disks...
<druel>

----- Original Message -----
From: "W. Wayne Liauh" <LiauhW001 at hawaii.rr.com>
To: "Linux & Unix Advocates & Users" <luau at list.luau.hi.net>
Sent: Monday, September 10, 2001 9:22 PM
Subject: [luau] Software Raid


> I saw software raid being mentioned on this board.  When I was doing
> disk partitioning with Roswell I noticed an option to make a partition
> Raid.  Does that mean that I can make a regular IDE hard disk operating
> raid without a raid controller? If yes, what level or levels are
> allowed?  Thanks.



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