Re: RAID 0+1 OR 1+0 ?

BELLANI, Gabriela said to 8 Oct 1998 14:15:36 GMT > What are the differences, advantages or disadvantages of: > >- Mirroring first and then stripping >over >- Generating stripe sets and then mirroring It depends if your RAID controller simply layers the RAID levels or if it has a specific 1+0 mode that integrates the levels. If you stripe then mirror a single drive failure takes out one side of the mirror which is a full stripe, i.e. half your drives. A second failure has a better than 50% chance of taking out the other side of the mirror. Replacing the drive implies that the mirror must be rebuilt which involves copying the surviving side of the mirror to the repaired side - even though it really only needed to copy one drive. If you mirror then stripe a single drive failure leaves only a relatively small part of the array with no backup. A second failure is only a problem if it happens to be the pair of the drive that first failed - much less than 50% risk. Replacing the drive means that only that drive will be copied from its mirror. In general, unless you *know* how smart the RAID controller is you should mirror then stripe. Even if you think you *know* you should ask yourself if you *trust* as well... Mike -- .----------------------------------------------------------------------. | Mike Jagdis | Internet: mailto:mike@roan.co.uk | | Roan Technology Ltd. | | | 54A Peach Street, Wokingham | Telephone: +44 118 989 0403 |