On Jan 11, 2012, at 5:01 AM, Jim Klimov wrote: > Hello all, I found this dialog on the zfs-de...@zfsonlinux.org list, > and I'd like someone to confirm-or-reject the discussed statement. > Paraphrasing in my words and understanding: > "Labels, including Uberblock rings, are fixed 256KB in size each, > of which 128KB is the UB ring. Normally there is 1KB of data in > one UB, which gives 128 TXGs to rollback to. When ashift=12 is > used for 4k-sector disks, each UB is allocated a 4KB block, of > which 3KB is padding. And now we only have 32 TXGs of rollback." > > Is this understanding correct?
Yes. -- richard > That's something I did not think of > previously, indeed... > > Thanks, > //Jim > > > http://groups.google.com/a/zfsonlinux.org/group/zfs-devel/browse_thread/thread/182c92911950ccd6/aa2ad1fdaf7d7a07?pli=1 > > On Aug 1, 2011, at 2:17 PM, Brian Behlendorf wrote: > > On Mon, 2011-08-01 at 10:21 -0700, Zachary Bedell wrote: > >> Given that uberblocks are 1k in size normally > >> and that they're supposed to be written out in single atomic > >> operations, does setting ashift=12 cause ZFS to pad out the uberblock > >> to 4k so that only one block is in each atomic write? Assuming it > >> does so, the label size must still be the normal 256k which would > >> leave fewer uberblock slots in the ring (32 instead of 128)? > > > Exactly right. When ashift=12 then the uberblock size is padded out > > to 4k. That means only 32 uberblocks fit in the on-disk space > > reserved for the ring. It's one of the lesser known side effects > > of increasing the ashift. > > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss -- ZFS and performance consulting http://www.RichardElling.com illumos meetup, Jan 10, 2012, Menlo Park, CA http://www.meetup.com/illumos-User-Group/events/41665962/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
