Topic: RAID6 -vesus- RAID5+SPARE

[Marco Hess]

I have not got a lot of experience in RAID systems (my systems so far have been RAID1 only) and I am getting a new system with 6 disks so I am looking at the options available.

A default install on this new system installs as a RAID5 + 1 spare. However, it could also be installed with the nospare option to get RAID6. I have read the various wiki and forum pages on the subject, but I am still a little lost on what the practical difference between RAID6 and RAID5+SPARE is.

As I understand it, RAID5 can handle a single drive failure and the hot spare would be used to switch from the failed drive to the hot spare and resync the array and then allow the failed drive to be swapped out (but requires the resync to be completed BEFORE the swap?).

Then RAID6 can handle 2 drive failures, so a failed drive can be swapped out immediately and even while syncing a second drive failure is still allowed to occur without a problem (and according to wikipedia, this allows for operator errors of swapping out the wrong drive ).

So why would you choose RAID5+1 (which is the default sme install mode) over RAID6 in a six drive system?

Marco

[paradigm]

I believe Raid 6 has lower write performance , (some where near a Raid 5 array with one disk missing) ,

Another point would be more load on the cpu (Raid 6 has to write two parity blocks which is one more then Raid 5).

I myself have no experience with Raid 5 or 6 with sme server , but from what i know hardware Raid is usually

recommended in a Raid 5 or larger setup...

[Marco Hess]

I believe Raid 6 has lower write performance , (some where near a Raid 5 array with one disk missing) ,

Another point would be more load on the cpu (Raid 6 has to write two parity blocks which is one more then Raid 5).

That makes sense. Thanks.

[Warlock]

As I understand it, RAID5 can handle a single drive failure and the hot spare would be used to switch from the failed drive to the hot spare and re-sync the array and then allow the failed drive to be swapped out (but requires the re-sync to be completed BEFORE the swap?)

if your controller is capable of hot swap then you can remove the failed drive anytime you want otherwise you need to power of the PC before you remove or swap disks. You can also start a raid5 without a spare connected, the downside is when 1 drive fails your array is in critical stage and still useable but you need to place a new drive in the array before a second drive failes.

raid 5 is Expandable you can start with an array of 3 disks and later add extra disks to the array without losing the data.
i started an raid5 array with 5 1TB disks and have now an array with 9 1TB disks. now i have 1 partition of 8TB available and i never had any data lost when i added 1 disk to expand my partition.
you also can migrate from raid5 to raid6 by adding 1 disk
raid6 is not capable of expanding or migrate to raid5

also keep in mind when your raid controller breaks down you will need to replace it with the same model or same raid family ( also keep a copy of the bios & firmware of the raid controller ) or you will lose your date ( buying 2 of the same controllers at the same time is not a bad idea )