Amount of drives in a Raid 5 Array?

[trmentry]

I currently have 2 raid5 arrays. 6 drives in one and 8 drives in the other. Each array has 1 drive set aside for a spare.

The 6 are 250s and the 8 are 320s. I've been tossing around getting 4 more 320s and switching out the 250s for those new 4. I was going to grow the 8 drives with the new 4 into a 12 disk array (1 spare). My question is: is there a point of diminishing returns on drives in a raid5 array? Would it be better to have 6 and 6?

This is in linux using software raid.

Thanks

 

[Farva]

When I did benchmarks between my 4x320 and my 8x320 arrays, my write speeds were about 10Mbps slower in the 8x320. I don't see why you wouldn't have 1 big array, but there are some things to worry about, more drives may be a higher failure rate to the array, meaning,

Failure rate * number of drives = dead array

If you have 2 arrays, in theory your data is kept safer overall than in one big one. But, I also have to say this now, keep backups. Raid =! backup

 

[oplin]

Depending on your card you should see better results with more drives. There are benchmarks on this all over the web just do a search for them. If you have a cheap low end card 2 arrays will probably be better than 1. Also consider going to Raid 6 if your card supports it. Also you should be able to install several raid cards in your system and have them all use 1 array so like 3 raid cards 1 array 12-24 disks you would probably see a significant rate of return with that setup granded you have the pcie slots open or pci whatever you are using.

If you are bandwidth limited on a pci bus not much is going to help you there cept more cards.

 

[trmentry]

Thanks for the info Oplin. Unfortunately no pcie slots for me, just pci. But I've desided to make 2 separate arrays. The biggest reason is I didn't want to have 5 drives in one case and 8 in the other. If either power supply pops, that takes out a big chunk of the drives and I'm afraid the array would suffer. So I'm going to keep the arrays built based on which case they are in.