On Thu, Mar 15, 2012 at 3:41 PM, Bob Friesenhahn <[email protected]> wrote: >> Yes, that's quite clear. But why it needs to READ from the pool while >> I'm only writing to the ZVOL (with dd)? > > > If your write requests do not perfectly overlap the underlying zfs blocks, > then zfs may need to read the existing block and modify it with your changed > data prior to writing it to a new place on disk. > > If the server has enough RAM, then it is likely that the existing data is > already cached in RAM so that zfs can do the update and write without > needing to access the disk first. Zfs loves RAM. > > It is useful to make sure that the zfs volume blocksize matches the I/O size > which is actually used, or is at least small enough that there is not > substantial read/write "amplification". >
That's a good argument, thank you :-) I will try with different volblocksize values and let you know. Regards, Simone. ------------------------------------------- illumos-discuss Archives: https://www.listbox.com/member/archive/182180/=now RSS Feed: https://www.listbox.com/member/archive/rss/182180/21175430-2e6923be Modify Your Subscription: https://www.listbox.com/member/?member_id=21175430&id_secret=21175430-6a77cda4 Powered by Listbox: http://www.listbox.com
