> the ZFS_Best_Practises_Guide states this: > > "Keep vdevs belonging to one zpool of similar sizes; Otherwise, as the > pool fills up, new allocations will be forced to favor larger vdevs > over smaller ones and this will cause subsequent reads to come from a > subset of underlying devices leading to lower performance." > > I am setting up a zpool comprised of mirrored LUNs, each one being > exported as a JBOD from my FC RAIDs. Now, as the zpool will fill up, I > intend to attach more mirrors to it and I am wondering, if I > understood that correctly. > > Let's assume I am creating the initial zpool like this: zpool create > tank mirror disk1a disk1b mirror disk2a disk2b mirror disk3a disk3b > mirror disk4a disk4b. After some time the zpool has filled up and I > attach another mirror to it: zpool attach tank mirror disk5a disk5b, > this would mean, that all new data would take a performance hit, since > it can only be stored on the new mirror disk, instead of being > distributed across all vdevs, right? > > So, to circumvent this, it would be mandantory to add at least as many > vdevs at once, to satisfy the desired performance?
If you make a pool and then fill it to > 80% or so, it will slow down. Then, if adding more drives to that pool, mirrors, raidz or whatever, new writes will basically be written to the new ones, since the rest of them arre full. To fix this, block rewrite needs to be implemented to create a way of balancing an existing pool, and I don't think the ZFS developers are there yet. To avoid this, replacing existing drives with larger drives (with autoexpand=on set on the pool) might be a solution. Vennlige hilsener / Best regards roy -- Roy Sigurd Karlsbakk (+47) 97542685 r...@karlsbakk.net http://blogg.karlsbakk.net/ -- I all pedagogikk er det essensielt at pensum presenteres intelligibelt. Det er et elementært imperativ for alle pedagoger å unngå eksessiv anvendelse av idiomer med fremmed opprinnelse. I de fleste tilfeller eksisterer adekvate og relevante synonymer på norsk. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
