RAID 5 (3 disks) or RAID 1

OK folks I recently lost dta located on a 500GB WD HDD. I had it spanned across several disks, therefore I recovered the lost data. I have now ordered three new 500GB disks with the idea of setting on RAID 5 on my P5B DLX. In discussing this with a fellow IT guru he mentioned I was making a bad move and should go with RAID 1 rather. His thoughts were the RAID 5 had to deal with the parity and offered the same fault tolerance as the mirror would. He felt I should stay with RAID 1 and keep the third for a replacement if ever need be. I guess I felt the RAID 5 was better based on three discs giving me a a more advantageous probability.....right? I figured there is a one in three chance of a disc going bad vs 1 of 2. Anyhow I realize I may get a performance hit with 5 vs
1 as well and understanding that 5 is also "hot swappable." Please give me your thoughts, either way I have three new discs just wondering now which array to go with. CYA!

For reliability over performance, an external backup + a RAID 1 mirror is far more reliable than any RAID array. (1) "RAID alone is not a backup"; external backups are better than RAID for data protection as far as the backups are recent enough. (2) "Bugs kill RAID dead". (3) RAID 1 is simpler therefore prone to fewer failures. (4) RAID 1 is simpler, therefore more portable and easier to recover from RAID implementation issues. (5) If drives have an equal chance of failure, then the odds of a failure among two drives is less than the odds of a failure among three drives. To understand this, perhaps compare a 1 drive system with a 1000 drives system. Which system would have the greater chance of a drive failure?

For performance over reliability, this greatly depends on the implementation details. Some RAID 5 implementations have huge performance issues with writes, esp. small writes -- much slower than single drives. RAID 1 implementations at worst behave slightly worse than single drives, roughly the same as a good approximation. RAID 5 implementations will typically have a significant performance advantage over single drives for reads, but really good RAID 1 implementations can also perform better than single drives for reads.

With a recent on-board Intel RAID implementation, I'd give the performance advantage to RAID 5, with the possible exception of small writes. I'd leave the final judgment on this to application tests that matter to you, using your implementation / configuration.

Bottom line: If you really want reliability, then do an external backup first, then optionally apply RAID 1. If you don't care so much about reliability, and care more about performance, then measure both, or just guess RAID 5.

I've did RAID 5 for a while, and have since changed back to RAID 1 (with offiste backup for all important stuff).

RAID 1 is much simpler, much faster (unless you spend $$$ for a real RAID card), and is the array does fall apart, you only need one working disk to get all your data back.

If a RAID 5 array goes wonky (ie: controller error - not disk error), then you lose everything.

With current hard drive capacities pushing past the 1TB barrier, I'd say RAID 5 is becoming more and more outdated outdated by the day.

Anything up to 1GB - RAID 1

Anything up to 2TB - RAID 10

Anything over 2GB - Then you either have too much porn, or your data is important enough to justify the cost of RAID 6.

Or use multiple smaller RAID 1 or RAID 10 arrays.

In your situation I would agree with both Madwand and your IT friend. Two disks in RAID 1, and the third for an external backup (or spare). If you find that 500Gb isn't enough you could pick up a forth and run RAID 10.

Is this to be a local array? Or a network file server?

Hehe

Keep in mind if you choose RAID 10 you are paying 2x as much for the same space.

Also in my personal experience I have never had a RAID 5 controller go 'wonky' it has always been the drives that go. In fact I have yet to have a single RAID 5 capable controller ever die. If companies were making crappy controller cards that would fink out and hose your data they would not be in business for very long

That being said with the cost of drives these days (and thier sizes) a Mirror is plenty and its very user friendly. Also the performance difference is RAID 1 is faster to write than RAID 5 but RAID 5 pushes ahead in the sustained read category which is why it often finds itself in large file servers. RAID 0 wins on both but provides less than no redundancy, RAID 10 is really only useful IMO when you are trying to get a larger mirrored volume, but with 750gig (and soon 1TB) drives in the market its overkill and more of a headache than it is worth.

PS- always turn the autorebuild feature off and run it manually if you need to rebuild your mirror.