Date: Fri, 17 Feb 2012 19:43:49 +0000 From: Alexander Best <arundel@freebsd.org> To: Julian Elischer <julian@freebsd.org> Cc: freebsd-fs@freebsd.org Subject: Re: freebsd-swap on ssd Message-ID: <20120217194349.GA36250@freebsd.org> In-Reply-To: <4F3EADDD.2010500@freebsd.org> References: <20120217141607.GA63659@freebsd.org> <4F3E9A14.3070605@freebsd.org> <20120217190921.GA26568@freebsd.org> <4F3EA75C.6070407@freebsd.org> <20120217193031.GA34283@freebsd.org> <4F3EADDD.2010500@freebsd.org>
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On Fri Feb 17 12, Julian Elischer wrote: > >On Fri Feb 17 12, Julian Elischer wrote: > >>On 2/17/12 11:09 AM, Alexander Best 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. > >>I think he meant ON A RAW FLASH DEVICE > >>SSD's have all that taken care of transparently. > >ahh is see. i wasn't aware of that. so in theory doing > > > >while true; do dd if=/dev/zero bs=4096 of=/dev/ssd count=1; done > > > >will not overwrite the first sector continuously, but the ssd controller > >will > >make sure the writes are being sprinkled all over the actual ssd? > > yes. that's the differnce between an SSD and a lump of flash soldered > onto a motherboard thanks for the info. it seems all my ufs on ssd related concerns were unnecessary then. cheers. alex > >cheers. > >alex > > > >>There are special file systems for raw flash devices that take all > >>that into account, > >>and ffs is not one of them. > >>
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