On Mon, May 28, 2012 at 6:13 PM, Daniel Carosone <d...@geek.com.au> wrote: > On Mon, May 28, 2012 at 09:23:25AM -0600, Nigel W wrote: >> After a snafu >> last week at $work where a 512 byte pool would not resilver with a 4K >> drive plugged in, it appears that (keep in mind that these are >> consumer drives) Seagate no longer manufactures the 7200.12 series >> drives which has a select-able sector size. The new 7200.14 series is >> 4k only. > > Does this mean they actually present with 4k sectors externally, > rather than use 4k internally and emulate 512b externally? If so, > this is a good thing - and good to know. > Based on the numbers stamped on drive and Seagate support, yes the 7200.14 present 4k sectors and the 7200.12 have a jumper that switches between 512 and 4k; though I don't know if that means the disk is 4k or 512 internally.
On Mon, May 28, 2012 at 6:13 PM, Daniel Carosone <d...@geek.com.au> wrote: > There are two problems using ZFS on drives with 4k sectors: > > 1) if the drive lies and presents 512-byte sectors, and you don't > manually force ashift=12, then the emulation can be slow (and > possibly error prone). There is essentially an internal RMW cycle > when a 4k sector is partially updated. We use ZFS to get away > from the perils of RMW :) > > 2) with ashift=12, whther forced manually or automatically because > the disks present 4k sectors, ZFS is less space-efficient for > metadata and keeps fewer historical uberblocks. > > For choosing a tradeoff today, I'll take 2 over 1, after experience > with both. 1 bites, seemingly especially with raidz types, but also > with mirrors. Also because a code change could at least improve the > metadata packing in future. > Yes that would suck the performance out and it is something that we have discussed at $work though so far it seems we have just lucked out and haven't seen the performance issues as a result of this. On Mon, May 28, 2012 at 6:13 PM, Daniel Carosone <d...@geek.com.au> wrote: > AFAIK, Hitachi is the only vendor still offering 512-native consumer > drives in the 2&3T sizes. They cost a little more, so that's another > tradeoff. Hmm. That is interesting to know. At very least another possible source of 512-byte drives if we need them for replacing drives in pools that are stuck with ashift=9. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
