> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
> boun...@opensolaris.org] On Behalf Of Bob Friesenhahn
> If almost all of the I/Os are 4K, maybe your ZVOLs should use a
> volblocksize of 4K?  This seems like the most obvious improvement.

Oh, I forgot to mention - The above logic only makes sense for mirrors and 
stripes.  Not for raidz (or raid-5/6/dp in general)

If you have a pool of mirrors or stripes, the system isn't forced to subdivide 
a 4k block onto multiple disks, so it works very well.  But if you have a pool 
blocksize of 4k and let's say a 5-disk raidz (capacity of 4 disks) then the 4k 
block gets divided into 1k on each disk and 1k parity on the parity disk.  Now, 
since the hardware only supports block sizes of 4k ... You can see there's a 
lot of wasted space, and if you do a bunch of it, you'll also have a lot of 
wasted time waiting for seeks/latency.

zfs-discuss mailing list

Reply via email to