On Sat, 23 Jan 2010, R.G. Keen wrote:
The reasoning came after reading the case for triple-parity raid. The curves showing time to failure versus time to resilver a single lost drive. Time to failure will remain constant-ish, while time to resilver will increase as the number of bits inside a single drive increases, largely because the input/output bandwidth is going to increase only very slowly. The bigger the number of bits in a single drive compared to the time to write a new, full disk worth of bits, the bigger the window for a second-drive failure. Hence, the third parity version is desirable.
Resilver time is definitely important criteria. Besides the number of raw bits to transfer from the drive, you will also find that today's super-capacity SATA drives rotate more slowly, which increases access times. Since resilver is done in (roughly) the order that data was written, access time will be important to resilver times. A pool which has "aged" due to many snapshots, file updates, and file deletions, will require more seeks. The smaller drives are more responsive so their improved access time will help reduce resilver times.
In other words, I think that you are making a wise choice. :-) Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
