Which raid set?

[eLbot]

I’m trying to figure out the best raid type for a group of 8 500GB drives.

I need a failure tolerance of one disk (storage takes priority over multiple drive failure protection) and a high read/write, although read takes priority over write.

I’m having a lot of trouble understanding the performance difference between raid 4 and 5, other that in normal conditions raid 4 is a faster read/write but on disk failure in the array, raid 5 would outperform a raid 4 array.

I’m currently looking at a raid 5+0, (2x 4drive raid 5's that are then raid 0'd) is this best option for 8 disks with my requirements of only one drive failure tolerance? (Raid 5+0 offers and unneeded two drive tolerance, one from each raid 5) but offers a higher read/write that most other solutions.

Cheers for the help.

-Will.

 

[Uhtred]

have you looked into RAID 1+0? Might not be ideal as you say capacity is an issue but i thought i'd mention it.

 

[eLbot]

The problem with raid 1+0 is that you lose half of the total available storage, so I'd end up with 2TB instead of the 3TB that a raid 5+0 would give, this also gives 4 drives of redundancy which I don't need.

I can really make do with one drive redundancy (or have to put up with the 2 drive redundancy that 5+0 offers) because if the array fails I can stop all use on the system and just allow it to rebuild, obviously i'll be taking the drives from a different production run to further reduce the likelihood of a double drive failure but I really don’t want to lose half my storage space, thanks for your input though.

Edit: Ah sneeky ninja edit you did there

 

[PieMaster]

7 disks in RAID5, then the remaining one as a hot spare?

Even if a drive breaks, it should be able to put the spare into the set before another fails.

 

[eLbot]

Ah, so it’s really a throw-up between an 8 drive RAID6 or a 7 drive RAID5 and 1 hot spare, as the performance differences are negligible? (I think, please correct me if I’m wrong, write speed is only hit by about 10% on RAID6 and the read speed is about the same) Then would it perhaps make more sense to have a RAID6 array with a drive on standby rather than an actual hot spare in case the worse happened?

Cheers for the help guys, think I’ll go with a RAID6. If someone thinks this is a bad idea let me know =P I have about a week before its implemented.