Yes, agreed and understood. It is a space reservation that ensures some number of blocks will never be allocated.
That's not exactly the same as them never being used, due to CoW updates, but it's very close. Once the pool is close to full, any writes that don't immediately free the original blocks will get denied. The net effect is the same: a relatively constant number of free blocks for the ssd controller to use in its own wear levelling and performance management. Overprovisioned storage with lots of spare blocks above whatever the device keeps internally already. At least, it seems so to me. My question, elaborated thus, is: what is the difference you see that makes it insufficient? Oh, are we not issuing TRIM from zfs as space is freed? That would explain it. If so, writing zeros into the reserved space (without compression, dedup, or snapshots) occasionally will tell the ssd controller the blocks are empty. I feel this is an effective workaround entirely within zfs, without resorting to the ugly tricks of multiple partitioning schemes and inflexible external allocations we both dislike. On 13 Apr 2016 18:27, "Dirk Steinberg" <[email protected]> wrote: > Am 13.04.2016 um 09:53 schrieb Daniel Carosone <[email protected] > >: > > What is wrong with a dataset with refreserv set? > > It does not actually reserve any specific blocks on the disk (LBAs for > SATA) which would > allow the SSD controller to deduct that a certain part of the SSD is not > being used. > > freservation is purely a (virtual) space accounting method of ZFS. > > *smartos-discuss* | Archives > <https://www.listbox.com/member/archive/184463/=now> > <https://www.listbox.com/member/archive/rss/184463/27748248-82bb0956> | > Modify > <https://www.listbox.com/member/?&;> > Your Subscription <http://www.listbox.com> > ------------------------------------------- smartos-discuss Archives: https://www.listbox.com/member/archive/184463/=now RSS Feed: https://www.listbox.com/member/archive/rss/184463/25769125-55cfbc00 Modify Your Subscription: https://www.listbox.com/member/?member_id=25769125&id_secret=25769125-7688e9fb Powered by Listbox: http://www.listbox.com
