>-----Original Message----- >From: Brandon High [mailto:bh...@freaks.com] >Sent: Monday, May 10, 2010 5:56 PM > >On Mon, May 10, 2010 at 3:53 PM, Geoff Nordli <geo...@gnaa.net> wrote: >> Doesn't this alignment have more to do with aligning writes to the >> stripe/segment size of a traditional storage array? The articles I am > >It is a lot like a stripe / segment size. If you want to think of it in those terms, >you've got a segment of 512b (the iscsi block size) and a width of 16, giving you >an 8k stripe size. Any write that is less than 8k will require a RMW cycle, and any >write in multiples of 8k will do "full stripe" writes. If the write doesn't start on an >8k boundary, you risk having writes span multiple underlying zvol blocks. > > >When using a zvol, you've essentially got $volblocksize sized physical sectors, but >the initiator sees the 512b block size that the LUN is reporting. If you don't block >align, you risk having a write straddle two zfs blocks. There may be some benefit >to using a 4k volblocksize, but you'll use more time and space on block checksums >and, etc in your zpool. I think 8k is a reasonable trade off. > > >If you're using the whole disk with zfs, you don't need to worry about it. If you're >using fdisk partitions or slices, you need be a little more careful. >
So... as long as you use whole disks, set the volblocksize to a multiple of the virtual machines file system allocation size, then you don't have to worry about alignment/optimization with ZFS. Thanks again!! Geoff _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
