On Fri, 2005-08-26 at 19:21 -0400, Guy wrote: > > > -----Original Message----- > > From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid- > > owner@xxxxxxxxxxxxxxx] On Behalf Of Dan Stromberg > > Sent: Friday, August 26, 2005 3:01 PM > > To: Linux RAID > > Cc: strombrg@xxxxxxxxxxxxxxx > > Subject: number of global spares? > > > > > > I've been working on a RAID setup with dual RAID controllers and > > three expansion boxes - 48 disks in all, including data, parity and > > global spares. > > > > We originally purchased the equipment expecting to get 16 terabytes of > > usable space. > > > > Now that it's "all set up", we're really seeing more like 14 or 15 > > terabytes, depending on how you do the calculation. > > > > Please be sure to use a fixed-pitch font when viewing the tables found > > below. BTW, if people weren't so terrified of HTML, I could just make a > > nice HTML table for easy reading without silly font requirements... > > > > Anyway, what we have right now is: > > > > global spares: 0,16,32,48 > > > > Raidset Disks used Data:parity ratio > > 0 1,2,3,4,5,6,7,8,9,10 9:1 > > 1 11,17,18,19,20,21,22,23,24,25 9:1 > > 2 26,27,33,34,35,36,37,38,39,40 9:1 > > 3 41,42,43,49,50,51,52,53,54,55 9:1 > > 4 56,57,58,59 3:1 > > > > > > And the vendor is suggesting that we move to something like: > > > > global spares: 0 > > > > Raidset Disks used Data:parity ratio > > 0 1,2,3,4,5,6,7,8,9,10 9:1 > > 1 11,17,18,19,20,21,22,23,24,25 9:1 > > 2 26,27,33,34,35,36,37,38,39,40 9:1 > > 3 41,42,43,49,50,51,52,53,54,55 9:1 > > 4 56,57,58,59,16,32,48 3:1 > > > > ...or...: > > > > global spares: 0,16 > > > > Raidset Disks used Data:parity ratio > > 0 1,2,3,4,5,6,7,8,9,10 9:1 > > 1 11,17,18,19,20,21,22,23,24,25 9:1 > > 2 26,27,33,34,35,36,37,38,39,40 9:1 > > 3 41,42,43,49,50,51,52,53,54,55 9:1 > > 4 56,57,58,59,32,48 3:1 > > > > > > Does anyone have any comments on: > > > > 1) The sanity of these 10 disk RAID 5's? > > > > 2) The degree of loss of reliability incurred by moving 3 disks from > > global spare to data? > > > > 3) The degree of loss of reliability incurred by moving 2 disks from > > global spare to data? > > > > > > To answer these questions, you probably need to know how the storage is to > > be used. This single, large filesystem will be used by a variety of > > researchers and students from around The University of California, Irvine, > > but was purchased primarily by the Earth System Science part of the > > Physical Sciences department, which in turn will primarily be storing many > > approximately 100 megabyte files which comprise time series related to > > climatology simulations. > > > > They don't feel that the storage has to be blazing fast, and 100% uptime > > isn't paramount, however they very much do not want to lose their data. > > > > The filesystem will not be backed up - we simply don't have anything large > > enough to back it up -to-, so if the some part of the storage solution > > goes kerflooey, we're totally... er... out of luck, and they'll probably > > be looking at me (the primary sysadmin on the storage configuration), > > wondering why their data is gone. > > RAID5, 6 or 1 is not data backup! It is hardware redundancy!! > Data loss or corruption can still occur with a RAID solution. RAID won't > help if someone fat fingers a "rm" command. > Corruption of the filesystem can also cause major data loss, without a > failed disk. Yeah. I know. > If the data was lost, what would it cost to re-create it? > Enough to buy a backup system? The data generated by the primary purpose for the hardware, will primarily be time series from models, that are hoped to match empirical data obtained from other sources. IE, it would take months or years to regenerate, but it could be regenerated. And people who have info under /data (this RAID rig) that they cannot lose, are advised to back it up somewhere themselves. - 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
