On Apr 13, 2010, at 11:57 AM, nate wrote: > John R Pierce wrote: > >> well, IF your controller totally screams and can rebuild the drives at >> wire speeds with full overlap, you'll be reading 7 * 2TB of data at >> around 100MB/sec average and writing the XOR of that to the 8th drive in >> a 8 spindle raid5 (14tb total). just reading one drive at wirespeed is >> 2000,000MB / 100MB == 20,000 seconds, or about 5.5 hours, so thats about >> the shortest it possibly could be done. > > More likely your looking at 24+ hours, because really no disk system > is going to read your SATA disks at 100MB/second. If your really lucky > perhaps you can get 10MB/second. > > With the fastest RAID controllers in the industry my own storage > array(which does heavy amounts of random I/O) averages about > 2.2MB/second for a SATA disk, with peaks at around 4MB/second. > > Our previous storage array averaged about 4-6 hours to rebuild > a RAID 5 12+1 array with 146GB 10k RPM disks, on an array that was > in excess of 90% idle. Rebuilding a 400GB SATA-I array often > took upwards of 48 hours. > > nate > > For a "real life" example, we have a 3 year old 12x 1TB SATA box using an Adaptec RAID controller, doing RAID 6 that takes about 3 days to rebuild the array each time a drive fails. Which, to date, has happened 10 times... (Fortunately, this is only a BackupPC box.) FWIW, we've not experienced a second drive failure during the rebuild process, yet. But we have had drives fail within a few weeks of each other, so it's probably going to happen one of these days.. -- Don Krause Head Systems Geek, Waver of Deceased Chickens. Optivus Proton Therapy, Inc. www.optivus.com "This message represents the official view of the voices in my head."