> One other question I have about using mirrors is > potential performance implications. > In a common scenario the user might be using the main > S(ATA) attached disk and > a USB external disk as a mirror configuration. Could > the slower disk become a > bottleneck because of it's lower I/O read/write > speeds? Would a system write block > until ZFS had written the data to both sides of the > mirror? > > Similarly, could the detached mirror device slow down > reads/writes because it's > doing extra work to cope with the missing mirror > device? > > Thanks, > Niall.
Yes to both I believe, while the USB device is attached your system will run slower, and it will run considerably slower while replicating data. Hopefully USB 3 or eSATA drives would address this to some extent. However, the idea of lop sided mirrors was discussed a while back in the availability thread (warning, it's long: http://www.opensolaris.org/jive/message.jspa?messageID=311743). There are many people who want ZFS to support lop sided mirrors, and I've tried to raise an RFE twice, but I don't believe I've ever seen a bug ID for it, it seems to get lost in the system. And yes, the resilver estimates are all over the place, even when you don't allow for the fact that it still restarts regularly. Would you be able to get away with just reporting the percentage complete and ignoring the estimates until that code is improved? Ross -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
