On Tue, May 17, 2011 at 11:48 AM, Jim Klimov <j...@cos.ru> wrote: >> So if you bump this to 32k then the fragmented size >> is 512k which tells ZFS to switch to a different metaslab >> once it drops below this threshold. > > Makes sense after some more reading today ;) > > What happens if no metaslab has a block this large (or small) > on a sufficiently full and fragmented system? Will the new writes > fail altogether, or a sufficient free space block would still be used?
If all the metaslabs on all of your devices won't accommodate the specified block then you will start to create gang blocks (i.e. smaller fragments which make up the specified block size). > > >> This is used to add more weight (i.e. preference) to specific >> metaslabs. A metaslab receives this bonus if it has an offset >> which is >> lower than a previously use metaslab. Sorry this is somewhat >> complicated and hard to explain without a whiteboard. :-) > > From recent reading on Jeff's blog and links leading from it, > I might guess this relates to different disk offsets with different > writing speeds? Yes-no would suffice, as to spare the absent > whiteboard ,) No. Imagine if you started allocations on a disk and used the metaslabs that are at the edge of disk and some out a 1/3 of the way in. Then you want all the metaslabs which are a 1/3 of the way in and lower to get the bonus. This keeps the allocations towards the outer edges. - George > > Thanks, > //Jim -- George Wilson M: +1.770.853.8523 F: +1.650.494.1676 275 Middlefield Road, Suite 50 Menlo Park, CA 94025 http://www.delphix.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
