Apologies - I missed that you were using SSDs as primary storage instead of SLOG.
Please disregard - Dave > On 14 Apr 2016, at 7:41 PM, Dave Finster <[email protected]> wrote: > > Hi Daniel > > I would recommend the 100G Hitachi SAS SSD SSD800MH.B - I’ve bought them for > $750 AUD and they fly. I’ve seen sequential writes of 476MB/sec and 512K > randoms at 313.5MB/sec. > > - Dave > >> On 14 Apr 2016, at 6:56 PM, Dirk Steinberg <[email protected] >> <mailto:[email protected]>> wrote: >> >>> >>> Am 14.04.2016 um 02:39 schrieb Richard Elling >>> <[email protected] >>> <mailto:[email protected]>>: >>> >>> >>>> On Apr 13, 2016, at 4:40 PM, Daniel Carosone <[email protected] >>>> <mailto:[email protected]>> wrote: >>>> >>>> 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? >>>> >>> no >>>> 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. >>>> >>>> >>> >>> pedantic question: why not buy good quality SSDs? >> >> Hmm, price? My 2TB 850 EVO cost me 530 EUR. >> How much would a „high quality“ SSD (say from Intel) cost? Maybe 2000 EUR? >> >> Also, availability in certain form factors (M.2) and capacities (I have >> never seen >> one of those HQ SSDs in 2 TB listed in a shop). >> >>> In my studies, good quality SSDs with >>> decent overprovisioning perform more consistently than el-cheapos. >> >> That is certainly true. >> >>> FWIW, the preponderance of the evidence suggests that wear out is not as >>> important as age. >>> COW file systems like ZFS are particularly well behaved. >>> https://www.usenix.org/conference/fast16/technical-sessions/presentation/schroeder >>> >>> <https://www.usenix.org/conference/fast16/technical-sessions/presentation/schroeder> >>> https://users.ece.cmu.edu/~omutlu/pub/flash-memory-failures-in-the-field-at-facebook_sigmetrics15.pdf >>> >>> <https://users.ece.cmu.edu/~omutlu/pub/flash-memory-failures-in-the-field-at-facebook_sigmetrics15.pdf> >>> >>> -- richard >>> >>>> On 13 Apr 2016 18:27, "Dirk Steinberg" <[email protected] >>>> <mailto:[email protected]>> wrote: >>>> Am 13.04.2016 um 09:53 schrieb Daniel Carosone <[email protected] >>>> <mailto:[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/184463/27861131-64318a9b> | > 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
