I can see how this would be useful. Being able to add disks over time, and of different sizes. The parity disk would be the biggest. Disks tend to get larger over time. So, when you add a disk it will tend to be larger than any of the others. The current parity would be re-used to extend the size, and the new disk would become the new parity. What would happen when you replace a failed disk with a new larger disk? Just waste the extra space? The performance would not be too good. Like raid5 on a real real bad day! I don't like concatenated disks. You can't balance the load on the drives. I would never use this feature if it did exist. But, some would love it I bet. Guy -----Original Message----- From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid-owner@xxxxxxxxxxxxxxx] On Behalf Of Tony Mantler Sent: Tuesday, September 07, 2004 12:53 PM To: linux-raid@xxxxxxxxxxxxxxx Subject: Concatenation with redundancy Hello, Recently I've seen a growing trend in creating very ad-hoc storage arrays for storing large quantities of media files (videos, music, etc). These arrays are usually initially created with a small number of concatenated drives, say 2 or 3, but over time can easily grow to span 6 or 8 drives as personal budgets allow. Obviously as time goes by the exposure to a single drive failure taking down the whole filesystem increases considerably, and I've seen this happen a number of times. Due to the size (frequently 1-2tb) and nature of data on the array, backup is usually impractical. It would seem that the current options for combining redundancy with flexible expansion capability leave a little to be desired. RAID 10 presents far too much wasted space for this type of application, and RAID 50 offers much less flexibility than is desired, and is still too inefficient for the number of drives in question. Thus the idea came to me for creating a somewhat new RAID level, which would be a concatenation with dedicated parity. Call it RAID 4C maybe, as in "RAID 4, but concatenated rather than striped". Thus, the data would appear as thus: drive 1 drive 2 .. parity drive block 1 ~ block N+1 .. = parity 1 block 2 ~ block N+2 .. = parity 2 .. block N ~ block N+M .. = parity N This would allow for inserting new drives without mangling the block order, thus preserving the data on the array. Ideally it would also be possible to create a heterogeneous array by ensuring that the parity drive was equal to or larger than the largest data drive, and assuming zeroed blocks for all non-present sectors. So, am I smoking crack here? Does anyone think this would be worth implementing? Has this already been implemented and I just haven't seen it? Cheers - Tony 'Nicoya' Mantler :) -- Tony 'Nicoya' Mantler -- Master of Code-fu -- nicoya@xxxxxx -- http://nicoya.feline.pp.se/ -- http://www.ubb.ca/ -- - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
