On Thursday 24 September 2009, Fajar Priyanto wrote: > Hi all, > Sorry for the OT. > I've got an IBM N3300-A10 NAS. It runs Data Ontap 7.2.5.1. > The problem is, from the docs it says that it only supports either > RAID-DP or RAID4. > What I want to achieve is Max Storage Capacity, so I change it from > RAID-DP to RAID4, but with RAID4, the maximum disk in a RAID Group > decrease from 14 to 7. In the end, either using RAID-DP or RAID4, the > capacity is the same. Both raid4 and raid5 could thoretically be used with 14 drives. Why they limit you to 7 drives at all is a good question (maybe you should ask IBM?). Possibly they consider too large arrays with only a single drive worth of parity un-safe. > Now, why RAID5 is not supported? I believe using RAID5, I can get more > storage capacity, can't I? > I also notice with some onboard RAID controller, they only support > either RAID0, RAID1, or RAID1+0. No RAID5. This has a completely different explanation. RAID0, 1 or 1+0 is a "simple" case of juggling sectors, no parity engine is needed. RAID4, 5 or 6 would require a much more complex and powerfull design. > What's wrong with RAID5, is there any technical limitation with RAID5? Compared to raid4: not much at all Compared to raid10: less safe, longer rebuilds, slower Compared to raid6: less safe, more usable space, typically faster /Peter
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