How does RAID 5 stack up?

man_from_uncle · 26 Jul 2006 at 11:08

Dear all,

I don't think i've ever posted to this particular part of the forum and my knowledge of hard disks is pretty paultry, so please go easy on me.

I have been running 3 80gig Hitachi SATA-II hard disks in RAID 5 since I built my PC at the beginning of the year and don’t really have anything to complain about. Having said that I have never been spoilt with good hard disks or any other type of RAID and I was wondering where this type of set up stands in relation to RAID 0, 1 and 0+1 and in relation to Raptors, either alone or in RAID. I’ve got the upgrade bug again and I thought I’d learn something in this area to see if there’s any cost effective upgrades I could make.

So basically, how good is my hard disk set up compared to the other options on the table?

Thanks,

Uncle

Imy · 26 Jul 2006 at 11:35

Not very I'd have to say. Onboard RAID 5 controller performance is usually poor.

There's a sticky at the top of this forum section that will explain the different types of RAID.

I wouldn't personally use RAID 5 outside of a file server. For a desktop system I would use RAID 0 or nothing. Your important data should all be backed up anyway.

I recommend a Raptor 37 or 74GB (16mb cache versions) for OS/applications and a Seagate Barracuda 320GB 7200.10 drive for data to most people. All depends on your requirements. You could always add another Raptor in RAID 0 for super-quick performance.

Mercutio · 26 Jul 2006 at 14:04

The above poster is SORT OF right. For data WRITES raid5 sucks badly with writes often being in the low -mid double figures range.
For reads it is nearly on par with raid0 (minus 1 disks performance).

Easiest way of telling is to HDtach the drive. Agreed with the above though - raid is an availabilty scheme NOT a backup scheme (hence why large companies run a tape-backup of their raid5) The raid is purely for the idea that it can survive the remainder of the day with slightly degraded performance before needing looking at. That or can survive while another drive is being quietly built back into the raid by the controller.

Personally im rather silly in that I run a raid0 without a particularly good backup scheme (ill just save important bits to another single drive) but do this knowing the consequences

Imy · 26 Jul 2006 at 14:13

Just re-read my post and I realised I made a blanket statemet - schoolboy error

I meant to say an onboard RAID 5 controller performance is usually poor when compared with a dedicated controller (hardware based).

I've typed it out a fair number of times on this forum and just get lazy

man_from_uncle · 26 Jul 2006 at 19:59

Thanks for that guys. So RAID5 writes pretty slow but it reads pretty fast, is that right? That would certainly fit in with my experiance....and with common sense for that matter if my understanding of how data gets striped and read is correct.

Imy · 26 Jul 2006 at 20:39

The problem is there can be a large difference between the theoretical performance you should get from using a specific type of RAID and the actual performance you get. It all depends on the hardware used.

With RAID 5 your writes should get faster as you add more disks but with a poor controller you could end up with write performance slower than a single drive on its own.