On 3/29/06 11:29 AM, "Hylton Conacher(ZR1HPC)"
Start with 4 disks, 3 in RAID 5 and the 4th as the mirror drive of the data on the RAID array. A month down the line take out one of the RAID drives, as though it had failed and replace it with a new one, store the 'faulty' disk for use later, the same way that a backup tape is stored before its MTBF point.
The following month buy another disk and again replace one of the RAID disks ie the mirrored one with the new one. Again store the 'failed' drive as before.
On month three 'fail' one of the drives and replace it with the 'failed' drive you took out on month 1.
And so on etc..etc....
The key is rotation and to backup from the mirrored drive as it will be the most up-to-date copy of the data sitting on the RAID array.
This is the only way I can see that your data will be safe from dual RAID drive failures. If that were to happen you could rebuild the RAID array from the mirrored drive as it is a copy of the data on the RAID array. If that too fails as it will without rotation, you will have to resort to your backup media.
This is a similar method we use with our main file share...(OSXS) and it works very well. You just have to remember to swap the drives at the specified time. You also have to make sure all your data will fit on one physical drive. We actually do this with three external "swap" drives. One hanging off the server, one in the firebox, and one at the home office in a firebox. They get rotated or swapped each week on Fridays. Just be prepared for some long "rebuild the raid" times depending on the amount of data. This is why we do it on Fridays. No one wants to work on Friday nights... ;) We have about 200 GB. We also then dup to another box in the office and stream to tape from that. Three sets of tape, and archive to DVD for individual projects. You can never have too many "backups". -- Thanks, George "They that would give up essential liberty for temporary safety deserve neither liberty nor safety." Benjamin Franklin