Skip Guenter wrote: > On Tue, 2009-06-02 at 16:36 +1000, Adam Goryachev wrote: > >> So, using 4 x 100G drives provides 133G usable storage... we can lose >> any two drives without any data loss. However, from my calculations >> (which might be wrong), RAID6 would be more efficient. On a 4 drive 100G >> system you get 200G available storage, and can lose any two drives >> without data loss. >> > > So isn't this the same as RAID10 w/ 4 drives, 200GB and can lose 2 > drives (as long as they aren't on the same mirror) and no risk of > corrupted parity blocks?
With RAID 10, if you loose a drive AND it's mirror, your array is toast. While you CAN loose two drives from a RAID 10 array, they have to be specific drives. With RAID 6 you have X data disks and 2 parity disks*. You can loose ANY two disks from a RAID 6 array without data loss. As you add more disks to a RAID 10 array, you have to dedicate half of them to mirroring. With a RAID 6 array, you only need two parity disks. Any more you add are usable to expand the capacity. Chris *This statement is simplified, in that neither RAID 5 nor RAID 6 actually dedicate a spindle (or two) to parity, but interleave it with the data. RAID 3 has a dedicated parity disk, but doesn't get much attention. With RAID 6, if you loose a disk, performance will not suffer, as no data is missing. RAID 5 down one disk and RAID 6 down two disks looses either a part of the data (which is calculated from the parity data) or the parity data. ------------------------------------------------------------------------------ OpenSolaris 2009.06 is a cutting edge operating system for enterprises looking to deploy the next generation of Solaris that includes the latest innovations from Sun and the OpenSource community. Download a copy and enjoy capabilities such as Networking, Storage and Virtualization. Go to: http://p.sf.net/sfu/opensolaris-get _______________________________________________ BackupPC-users mailing list BackupPC-users@lists.sourceforge.net List: https://lists.sourceforge.net/lists/listinfo/backuppc-users Wiki: http://backuppc.wiki.sourceforge.net Project: http://backuppc.sourceforge.net/