First thing, we’re using Intel DC S3700 SSDs as ZILs in all our SmartOS hypervisors and have noticed a marked difference in write performance, especially on MySQL VMs, where the abundance of IOPS really helps. The key thing to look out for is how the drive itself caches written data - as I understand it, the majority of consumer grade drives aggressively cache writes in volatile memory which renders the (committed) data lost in the event of a power-cut. Intel seems to refer to it as “Enhanced Power Loss Protection” on their spec sheets:
http://ark.intel.com/products/71913/Intel-SSD-DC-S3700-Series-100GB-2_5in-SATA-6Gbs-25nm-MLC > And it seems like how A Toponce does it makes sense : get 2 good quality > (but not necessarily large) SSDs and partition them into 2 areas: one > "fairly" small for the SLOG and the other larger partition for the L2ARC ... > ?? > > In his case he did 5GB for the SLOG and the rest (45GB) for the Cache .. > > Seems like a good use of resources? I’ll paste what Keith Wesolowski helpfully replied when I asked something similar on the list a while back: > I never recommend using partitions with ZFS, and that includes slogs. > It's not "dangerous" per se; it ought to work and I'm sure there are > plenty of home users doing it successfully. But it makes it much more > difficult to understand performance data, the two workloads can actively > interfere with one another, will affect the unobservable and invariably > buggy firmware behaviour of the device and its flash controller, and > (though this is much more relevant for spinning disks with their write > caches) there are settings that can only be applied to a physical > device. > > These devices are inexpensive, so while 100 GB is certainly overkill for > a slog, the proper economic calculus is how much performance you get for > a dollar or a euro, given that the device is sufficiently capacious to > satisfy your endurance requirements. Not 5 years ago we were paying > $6000+ for 10k WIOPS; today you can get more than that for $250. Just > pretend it's a 10 GB or 20 GB device (whatever size you think is the > most you'll need; anywhere in that range is surely plenty) that lasts 5x > as long and be thrilled by what Moore's Law has given you. Trying to > extract every last dime of value from it, especially if you don't > already know that another 160 GB or so of L2ARC will make a difference > anyway, has always seemed to me to be penny-wise and pound-foolish. > And, somewhat paradoxically, this becomes even more true as your > performance needs and SSD count increase; seriously high performance > requirements are driven by highly valuable business needs. The more > important the task, the less it makes sense to take on operational risk > in exchange for a modest reduction in cost. So, it depends on what you’re doing, but from our point of view it totally makes sense :) Thomas. > On May 8, 2014, at 12:50 AM, Dennis Jun via smartos-discuss > <[email protected]> wrote: > >> What do you mean by "super hard"? ZeusRAM is generally the best for a SLOG. >> >> I think the Samsung 840 is still consumer grade and also sata. The s-tec 840 >> is enterprise grade for L2ARC and SAS. >> (http://www.hgst.com/solid-state-storage/enterprise-ssd/sas-ssd/s840-sas-ssd) >> >> >> From: Ibrahim Tachijian via smartos-discuss >> Sent: Thursday, May 8, 2014 00:31 >> To: [email protected] >> Reply To: [email protected] >> Subject: [smartos-discuss] ZIL recommendations >> >> Googling your way through any recommendation for a good ZIL (other than the >> ZeusRam) seems super hard. >> >> Can somebody recommend something that stores still stock and would be >> considered a good buy to use as a ZIL? >> >> For the L2ARC I'm going to go with the samsung 840 pro unless someone has >> any other recommendation. >> >> -- >> Ibrahim Tachijian >> smartos-discuss | Archives | Modify Your Subscription >> >> smartos-discuss | Archives | Modify Your Subscription > > smartos-discuss | Archives | Modify Your Subscription ------------------------------------------- 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
