>-----Original Message----- >From: Brandon High [mailto:bh...@freaks.com] >Sent: Monday, May 10, 2010 9:55 AM > >On Sun, May 9, 2010 at 9:42 PM, Geoff Nordli <geo...@gnaa.net> wrote: >> I am looking at using 8K block size on the zfs volume. > >8k is the default for zvols. >
You are right, I didn't look at that property, and instead I was focused on the record size property. >> I was looking at the comstar iscsi settings and there is also a blk >> size configuration, which defaults as 512 bytes. That would make me >> believe that all of the IO will be broken down into 512 bytes which >> seems very inefficient. > >I haven't done any tuning on my comstar volumes, and they're using 8k blocks. >The setting is in the dataset's volblocksize parameter. When I look at the stmfadm llift-lu -v .... it shows me the block size of "512". I am running NexentaCore 3.0 (b134+) . I wonder if the default size has changed with different versions. > >> It seems this value should match the file system allocation/cluster >> size in the VM, maybe 4K if you are using an ntfs file system. > >You'll have more overhead using smaller volblocksize values, and get worse >compression (since compression is done on the block). If you have dedup >enabled, you'll create more entries in the DDT which can have pretty disastrous >consequences on write performance. > >Ensuring that your VM is block-aligned to 4k (or the guest OS's block >size) boundaries will help performance and dedup as well. This is where I am probably the most confused l need to get straightened in my mind. I thought dedup and compression is done on the record level. As long as you are using a multiple of the file system block size, then alignment shouldn't be a problem with iscsi based zvols. When using a zvol comstar stores the metadata in a zvol object; instead of the first part of the volume. As Roy pointed out, you have to be careful on the record size because DDT and L2ARC lists consuming lots of RAM. But it seems you have four things to look at: File system block size -> Iscsi blk size -> zvol block size -> zvol record size. What is the relationship between iscsi blk size and zvol block size? What is the relationship between zvol block size and zvol record size? Thanks, Geoff _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
