Will RAID do me any good?

jstech · 2005-11-01 07:59:05

I'm curious about giving software RAID a try (after learning about RAID in my Operating Systems course), but I know that the performance increase depends largely on how your hardware is set up. I have two harddrives. One is IDE, the other is SATA, which is on a PCI controller card. I have plenty of space, so I was planning to just use RAID 1 for my root and swap partitions.

Would software RAID give me better performance?

SamuraiDan · 2005-11-01 08:41:10

jstech wrote:

I was planning to just use RAID 1 for my root and swap partitions.
Would software RAID give me better performance?

RAID 1 is mirroring so you would get get no performance benifit ftom it. You should get an increase from RAID 0 (striping) or one of the higher levels, but I am personally unsure of how (or if) it would work with your hardware setup. Also are you sure you can use software raid on individual partitions rather than the whole disk?

T-Dawg · 2005-11-01 12:42:47

Last I knew you had to have identical hard-drives for stiping to work, you may want to research that before anything. Another thing, with striping your going to have potentionaly twice the failure rate because you're using two seperate hard-drives to write different pieces of information. If you have one drive go up on you, the remaining info on the other drive is not enough to be used anymore and you data is pretty much lost.
If you do decide to use this set up make sure your hard drives will work together and you have a good UPS to supply steady power to them. Brownouts are the silent killers to hard drives.

jstech · 2005-11-01 16:20:23

Thanks for the advice.

RAID 1 doubles your read speed, because you can read half from each disk. After more thought, I figure I'll try RAID 0 for the swap partition (where speed is most important anyway), but stick with RAID 1 for root, so I have the data redundancy.

Mythoz · 2005-11-01 18:27:41

jstech wrote:

I'll try RAID 0 for the swap partition (where speed is most important anyway)

You do not need any RAID setup for swap area (especially not software RAID, which introduces some extra overhead). Just create two swap partitions. One on the first harddrive and the other on the second. They even don't need to be the same size. Linux will distribute the swap pages in a round-robin manner: first page will go to the first swap partition, second to the the second, third to the first again and so on.

Look at the man pages of swapon:

# man swapon
# man 2 swapon

Lone_Wolf · 2005-11-01 22:51:22

mdadm can create sw raid arrays from partitions, you just have to make them equal in size.

I use LVM2 with 6 logical volumes on my pc. at first i just used vgextend to combine 2 hd's to one big volume, then i found out lvm can use raid arrays as physical volumes.

I setup those 2 hd's as a sw raid 0 now, and got a nice increase of speed.

since i backup my important data and user settings regularly on usb-hd / dvd , i don't mind the increased risk of failure that comes with raid 0.

If you want to be safe and have speed, get 4 hd's of the same size and make a raid 1+0 array with them.
(that was a bit too expensive for me).

RedShift · 2005-11-06 17:55:11

Don't forget when using RAID your access time almost triples. RAID 0 is only good for servers that need to transfer vast amounts of large files.

Gullible Jones · 2005-11-13 22:50:58

I thought read performance on RAID 1 was better?

Lone_Wolf · 2005-11-14 22:59:26

http://www.pcguide.com/ref/hdd/perf/rai … single.htm

copied from the above page for Raid 0

Random Read Performance: Very good; better if using larger stripe sizes if the controller supports independent reads to different disks in the array.

Random Write Performance: Very good; again, best if using a larger stripe size and a controller supporting independent writes.

Sequential Read Performance: Very good to excellent.

Sequential Write Performance: Very good.

Recommended Uses: Non-critical data (or data that changes infrequently and is backed up regularly) requiring high speed, particularly write speed, and low cost of implementation. Audio and video streaming and editing; web servers; graphic design; high-end gaming or hobbyist systems; temporary or "scratch" disks on larger machines.

Arch Linux

#1 2005-11-01 07:59:05

Will RAID do me any good?

#2 2005-11-01 08:41:10

Re: Will RAID do me any good?

#3 2005-11-01 12:42:47

Re: Will RAID do me any good?

#4 2005-11-01 16:20:23

Re: Will RAID do me any good?

#5 2005-11-01 18:27:41

Re: Will RAID do me any good?

#6 2005-11-01 22:51:22

Re: Will RAID do me any good?

#7 2005-11-06 17:55:11

Re: Will RAID do me any good?

#8 2005-11-13 22:50:58

Re: Will RAID do me any good?

#9 2005-11-14 22:59:26

Re: Will RAID do me any good?

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