Thanks for the insight, Richard. -- Sriram
On Thu, Aug 8, 2013 at 8:41 PM, Richard Elling < richard.ell...@richardelling.com> wrote: > On Aug 7, 2013, at 2:50 PM, Jason Lawrence <jjlaw...@gmail.com> wrote: > > > This might be a better question for the Illumos group, so please let me > know. > > > > I have a zvol for a KVM instance which I felt was taking up too much > space. After doing a little research, I stumbled upon > http://support.freenas.org/ticket/2383 and repeated the test on my > machine. I'm running a RAIDZ2 pool with eight "advanced format" 4k sector > drives. I created the pool with ashift=12 with this in mind. > > > > root@hostname:~# zfs create -V 20g -o volblocksize=32k > storage/testbed/32k > > root@hostname:~# zfs create -V 20g -o volblocksize=8k storage/testbed/8k > > > > root@hostname:~# dd if=/dev/zero of=/dev/zvol/rdsk/storage/testbed/32k > bs=1048576 count=20400 > > 20400+0 records in > > 20400+0 records out > > 21390950400 bytes (21 GB) copied, 493.836 s, 43.3 MB/s > > > > root@hostname:~# dd if=/dev/zero of=/dev/zvol/rdsk/storage/testbed/8k > bs=1048576 count=20400 > > > > 20400+0 records in > > 20400+0 records out > > 21390950400 bytes (21 GB) copied, 548.916 s, 39.0 MB/s > > > > root@hostname:~# zfs list | grep testbed > > storage/testbed 64.2G 5.79T 307K /storage/testbed > > storage/testbed/32k 21.3G 5.79T 21.3G - > > storage/testbed/8k 42.8G 5.79T 42.8G - > > > > > > The 8k blocksize zvol takes up twice the space of the 32k blocksize > zvol. As 8k is the default, this must be affecting others... > > This is expected. For 4K sector sizes and > 9 disks per raidz2 set: > volblocksize = 8k, raidz2 writes 2 data (8k) + 2 parity (8k) > [like mirroring] > volblocksize = 32k, raidz2 writes 8 data (32k) + 2 parity (8k) > [like RAID-6] > > What most folks miss is: > volblocksize = 4k, raidz2 writes 1 data (4k) + 2 parity (8k) [like > triple mirroring] > > so, don't do 4k recordsize with 4K sector disks unless you are mirroring. > -- richard > > -- > > richard.ell...@richardelling.com > +1-760-896-4422 > > > > _______________________________________________ > OpenIndiana-discuss mailing list > OpenIndiana-discuss@openindiana.org > http://openindiana.org/mailman/listinfo/openindiana-discuss > -- Belenix: www.belenix.org _______________________________________________ OpenIndiana-discuss mailing list OpenIndiana-discuss@openindiana.org http://openindiana.org/mailman/listinfo/openindiana-discuss
