Date: Fri, 17 Feb 2012 11:43:25 -0800 From: Julian Elischer <julian@freebsd.org> To: Alexander Best <arundel@freebsd.org> Cc: freebsd-fs@freebsd.org Subject: Re: freebsd-swap on ssd Message-ID: <4F3EADDD.2010500@freebsd.org> In-Reply-To: <20120217193031.GA34283@freebsd.org> References: <20120217141607.GA63659@freebsd.org> <4F3E9A14.3070605@freebsd.org> <20120217190921.GA26568@freebsd.org> <4F3EA75C.6070407@freebsd.org> <20120217193031.GA34283@freebsd.org>
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> 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 > 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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