On Mon, 2009-06-22 at 06:06 -0700, Richard Elling wrote: > Nevertheless, in my lab testing, I was not able to create a random-enough > workload to not be write limited on the reconstructing drive. Anecdotal > evidence shows that some systems are limited by the random reads.
Systems I've run which have random-read-limited reconstruction have a combination of: - regular time-based snapshots - daily cron jobs which walk the filesystem, accessing all directories and updating all directory atimes in the process. Because the directory dnodes are randomly distributed through the dnode file, each block of the dnode file likely contains at least one directory dnode, and as a result each of the tree walk jobs causes the entire dnode file to diverge from the previous day's snapshot. If the underlying filesystems are mostly static and there are dozens of snapshots, a pool traverse spends most of its time reading the dnode files and finding block pointers to older blocks which it knows it has already seen. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
