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. 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. What's wrong with RAID5, is there any technical limitation with RAID5? Thanks.
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. > > Now, why RAID5 is not supported? I believe using RAID5, I can get more > storage capacity, can't I? >Design/marketing decision for the features of the board?> I also notice with some onboard RAID controller, they only support > either RAID0, RAID1, or RAID1+0. No RAID5. >They do not want to go through the trouble of implementing raid5 for that particular board or they want raid5 to be available on more expensive options or ...etc> What's wrong with RAID5, is there any technical limitation with RAID5? >Not with the technology itself. They are just not offering raid5. If you have a problem with that, get another product or go to another company.
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 -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 189 bytes Desc: This is a digitally signed message part. URL: <http://lists.centos.org/pipermail/centos/attachments/20090924/dfc0e22c/attachment.sig>
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. > > 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. > > What's wrong with RAID5, is there any technical limitation with RAID5?I think that's a re-branded Netapp FAS 2020. NetApps let you grow volumes by simply adding disks and with raid4 if you initialize the new disk to all zero's you don't have to recompute/rebuild the parity which is on a separate disk. That doesn't work with raid5. It's probably the wrong device if your first concern is being cheap. -- Les Mikesell lesmikesell at gmail.com
Am 24.09.2009 um 07:43 schrieb Fajar Priyanto:> 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. > > 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. > > What's wrong with RAID5, is there any technical limitation with RAID5?Well, it depends on the disk-size: http://www.enterprisestorageforum.com/technology/features/article.php/3839636 Rainer
[re-sending with the right email address, hoping the first email won't make it through..] 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-DPor RAID4.> What I want to achieve is Max Storage Capacity, so I change it fromRAID-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. It's the array's way of saying it's not really safe to operate a 14 disk RAID-4 group in the event of a drive failure. Also performance will suffer greatly with such a large data:parity drive ratio. NetApp RAID DP (what you have): http://www.netapp.com/us/library/white-papers/wp_3298.html> What's wrong with RAID5, is there any technical limitation with RAID5?Most onboard RAID controllers are absolute crap, RAID 5 isn't as easy to support as RAID1/RAID0, as extra processing time and code is needed for the parity stuff. I wouldn't use them for even RAID 1 though. If it's onboard, and I want RAID then I'll use software RAID. Unless it's a SCSI/SAS RAID controller often times those onboard RAID controllers are of decent quality. RAID 5 as implemented by most disk vendors does have issues at least with large SATA disks - Why RAID 5 stops working in 2009 - http://blogs.zdnet.com/storage/?p=162 A couple vendors that I know of - 3PAR(which I use) and Compellent don't suffer from this limitation because they virtualize the disks, I can't speak too much for Compellent's architecture but 3PAR doesn't RAID physical disks, they raid portions of each disk, when a disk fails, every disk in the system participates in rebuilding that failed set of arrays, which results in upwards of a 10x improvement in recovery time and 90%+ drop in system impact while the arrays are rebuilding. This virtualization also allows you to run multiple levels of RAID on the same spindles for different purposes. The likelihood of suffering a double disk failure on such a system during a RAID rebuild is probably quite a bit less than suffering a triple disk failure on a RAID-6 system which runs RAID on whole physical disks. At full system load my array can recover from a 750GB drive failure in less than 3 hours. Our previous array took nearly 30 hours to recover from a 300GB(SATA) drive failure. If on my array the disk is only half utilized, then it will take half the time to rebuild, as only written data is rebuilt, no point in replicating portions of the disk that haven't been used, though other vendors do this because they don't have the architecture to support sub-disk rebuilds. My own 200-disk array has more than 86,000 individual RAID arrays on it, most of them being RAID 5(5+1). Array management is automatic and transparent to the storage system I just tell it how big a volume I want and what type of data protection. For performance reasons I'm migrating my RAID 5(5+1) to 3+1 next year after I add more space. I miscalculated the growth of the big driver of space on the current system so I had to migrate to 5+1(RAID level migrations have no service impact either on my array). On my system there is roughly only a 9% performance drop from RAID 1+0 to RAID 5+0, so in many cases running RAID 5 on my array is about the same as RAID 1 on other arrays, it's that fast. RAID 6 has a pretty good performance hit vs RAID 5 due to the extra parity disk, on some arrays the performance hit is even greater as the array calculates parity twice, NetApp I think has as good a RAID 6 implementation as there is, though they can't get around writing the parity information to two different disks. nate