Date: Sat, 18 Feb 2012 12:18:45 +0100 From: "Ronald Klop" <ronald-freebsd8@klop.yi.org> To: freebsd-fs@freebsd.org Subject: Re: freebsd-swap on ssd Message-ID: <op.v9vgdj1s8527sy@pinky> In-Reply-To: <20120217190921.GA26568@freebsd.org> References: <20120217141607.GA63659@freebsd.org> <4F3E9A14.3070605@freebsd.org> <20120217190921.GA26568@freebsd.org>
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On Fri, 17 Feb 2012 20:09:21 +0100, Alexander Best <arundel@freebsd.org> wrote: > On Fri Feb 17 12, Julian Elischer wrote: >> On 2/17/12 6:16 AM, Alexander Best wrote: >> >hi there, >> > >> >putting a freebsd-ufs partition on an ssd isn't recommended, since the >> ufs >> >structure (unlike zfs e.g.) requires certain data to be continuously >> >written to >> >a fixed location and thus will cause the ssd to quickly run out of >> >write-cycles >> >and die. >> nonsense. >> the SSD doesn't use the same flash for the same logical locatio each >> time! >> it maps it to different locations each time. > > i simply repeated what kirk mckusick said in the SU+J introduction > video. he > said for exactly this reason ufs should not be used on an ssd, since > stuff like > inode entries live in a fixed location, whereas with zfs the ueberblock > can > live in 128 locations. also in case of SU+J, where the journal only > takes up a > very small part of the disk due to the fact that it's only tracking > metadata > changes and isn't doing logging (like gjournal), there's also the chance > to run > out of write-cycles. A related question. Does journaling make sense on a ssd? I don't think there is a write cache on the ssd. Ronald. > > see: http://youtu.be/_NuhRkiInvA > > cheers. > alex > >> >> >but how about using a small ssd (approx. 10GB) as one entire >> freebsd-swap >> >partition? will this make more sense, or are there certain structures >> >within >> >the freebsd-swap partition type, which also need to be continuously >> >written to >> >a fixed location? >> small SSDs may have less wear resistance than big ones.. the cheap >> ones may not even >> use proper mapping.. >> >another question i'd like to ask: are there also issues with >> read-cycles on >> >ssds? because i was thinking about putting a freebsd-boot partition on >> an >> >ssd >> >drive and only mounting it ro. this should solve the write-cycle issue >> in >> >theory. however i'm not sure, if stuff like the dirty bit or the ufs >> label >> >will >> >also remain untouched. so even though the partition will only be >> mounted >> >ro, >> >freebsd might still frequently write certain data to a fixed location >> on >> >the >> >ssd drive which hosts the freebsd-boot partition. if this is the case, >> is >> >there >> >a way of completely prohibiting any writes to a disk? will revoking any >> >write >> >permissions from the device entry under /dev guarantee this, or is >> using a >> >any >> >device 100% ro under freebsd impossible (unless it has a hardware >> switch to >> >forbid writes)? >> >> yes there are small issues with read cycles but it is all hidden from >> you by the drive. >> >cheers. >> >alex >> >_______________________________________________ >> >freebsd-fs@freebsd.org mailing list >> >http://lists.freebsd.org/mailman/listinfo/freebsd-fs >> >To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org" >> > > _______________________________________________ > freebsd-fs@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-fs > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org"
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