On Wed, Jul 22, 2009 at 02:45:52PM -0500, Bob Friesenhahn wrote: > On Wed, 22 Jul 2009, t. johnson wrote: > >Lets say I have a simple-ish setup that uses vmware files for > >virtual disks on an NFS share from zfs. I'm wondering how zfs' > >variable block size comes into play? Does it make the alignment > >problem go away? Does it make it worse? Or should we perhaps be > > My understanding is that zfs uses fixed block sizes except for the > tail block of a file, or if the filesystem has compression enabled.
For one block files, the block is variable, between 512 bytes and the smaller of the dataset's recordsize or 128KB. For multi-block files all blocks are the same size, except the tail block. But these are sizes in file data, not actual on-disk sizes (which can be less because of compression). > Zfs's large blocks can definitely cause performance problems if the > system has insufficient memory to cache the blocks which are accessed, > or only part of the block is updated. You should set the virtual disk image files' recordsize (or, rather, the containing dataset's recordsize) to match the preferred block size of the filesystem types (or data) that you'll put on those virtual disks. Nico -- _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
