From owner-freebsd-fs@FreeBSD.ORG  Fri Feb 17 19:30:31 2012
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Date: Fri, 17 Feb 2012 19:30:31 +0000
From: Alexander Best <arundel@freebsd.org>
To: Julian Elischer <julian@freebsd.org>
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Subject: Re: freebsd-swap on ssd
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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?

cheers.
alex

> 
> There are special file systems for raw flash devices that take all 
> that into account,
> and ffs is not one of them.
>