The 840 EVO does NOT have cache power protection and is useless as a log device.
Every write to them will be given a cache flush, which will be honored by the Samsung SSD and flush the cache. This tremendously slows them down because they get great advantages by caching all their writes. You will also kill them in rapid fashion because you are forcing many read modify writes on a TLC SSD. You can override this in the sd.conf, but in that case you might as well use sync=disabled at the zfs level and skip the ZIL all together, because the 840 EVO is NOT going to have the logs you just sent to them in a power failure. The 840 EVO is a great cache device, but not a log device. You need a write oriented SSD with power loss protection such as the Intel DC S3700 or ZeusRAM. If all you want is performance at the expense of power loss protection, just shut off the ZIL with the sync=disabled parameter. This will be faster than even a bunch of ZeusRAMs as log devices. -Chip On Mon, Oct 20, 2014 at 4:02 AM, Ian Collins via smartos-discuss < [email protected]> wrote: > Andre Sachs wrote: > >> Hi Ian, >> >> I am in the process of testing my pool with synchronous 4k writes and >> various thread numbers. >> How do you have your pools configured to with the Evo's as logs ? >> >> I used my usual stripe of spinning rust mirrors and one or two (striped) > log devices. > > As I said before, I don't ant wouldn't recommend using them as logs in > production. > > > -- > Ian. > > > > ------------------------------------------- > smartos-discuss > Archives: https://www.listbox.com/member/archive/184463/=now > RSS Feed: https://www.listbox.com/member/archive/rss/184463/ > 26131723-5e6842d7 > Modify Your Subscription: https://www.listbox.com/ > member/?& > Powered by Listbox: 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
