Date: Sat, 19 Jan 2019 14:00:47 -0600 From: jdelisle <jdelisle@gmail.com> To: Ira Cooper <ira@wakeful.net> Cc: Maciej Jan Broniarz <gausus@gausus.net>, freebsd-fs@freebsd.org Subject: Re: ZFS on Hardware RAID Message-ID: <CAMdBLfQ5cWfxUuVCe5-RnKJhgzTgFeGff=HJQ_rBB%2B%2BsaVH93w@mail.gmail.com> In-Reply-To: <CAAPGDwKtnpP_J6qVeUOoLYai%2BX3KMcCnvXSCCiruUhFM4uYDTA@mail.gmail.com> References: <1180280695.63420.1547910313494.JavaMail.zimbra@gausus.net> <92646202.63422.1547910433715.JavaMail.zimbra@gausus.net> <CAAPGDwKtnpP_J6qVeUOoLYai%2BX3KMcCnvXSCCiruUhFM4uYDTA@mail.gmail.com>
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Wouldn't a write-back cache (battery-backed) improve write performance? Assuming the cache is sufficiently sized for the workload, would it not have an effect similar to ZIL, meaning low-latency persisted writes? On Sat, Jan 19, 2019 at 1:41 PM Ira Cooper <ira@wakeful.net> wrote: > On Sat, Jan 19, 2019 at 11:43 AM Maciej Jan Broniarz <gausus@gausus.net> > wrote: > > > Hi, > > > > I want to use ZFS on a hardware-raid array. I have no option of making it > > JBOD. I know it is best to use ZFS on JBOD, but > > that possible in that particular case. My question is - how bad of an > idea > > is it. I have read very different opinions on that subject, but none of > > them seems conclusive. > > > > Any comments and especially case studies are most welcome. > > All best, > > > > I've actually built Illumos based ZFS NAS systems based on raid controllers > and non-raid controllers. > > If given the choice, I'd use non-raid controllers, today. (HBAs) > > Why? Because ZFS handles the "raid" layer well. The write back cache a > RAID controller provides, isn't really needed with ZIL, nor desired. > > All a raid controller really brings in my experience is added operational > complexity once you use good enough hardware, mainly good ZIL drives and > HBAs. > > So it isn't really a "bad" idea, more just redundant, expensive and > inconvenient. You could have good reasons to do it, like that the RAID > controller is built into the motherboard etc. > > Just make sure your data integrity is #1. Writeback caches are properly > battery protected, or not used. etc. > > Best, > > -Ira > _______________________________________________ > freebsd-fs@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-fs > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org" >
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