SSD for boot and swapcache

Tim Darby t+dfbsd at
Fri Dec 3 11:50:39 PST 2010

Cool and thanks for the tip about root chaining.  I wasn't aware of that feature.Tim
On Fri, Dec 3, 2010 at 12:26 PM, Matthew Dillon <dillon at> wrote:

:I'm thinking of setting up a 40GB Intel SSD as both the boot drive and
:swapcache.  Is this a reasonable thing to do?  Are there any gotchas or
:things I need to watch out for as I set this up?  I'd like to have /boot as
:UFS and the rest of / as Hammer (the way the installer does it) and have /
:on a different drive.

    Perfectly acceptable in my view.  I would partition it 700MB for /boot,
    1G reserved for an emergency root, and 32G for swap/swapcache.  Leave ~6G
    unused at the end which you never write to ever (if this is a
    fresh SSD).

    Another option, another reason why I suggest reserving 1G for an
    emergency root, is that Alex has that root chaining feature in the
    system now for dealing with encrypted root drives.  The concept can
    be used whether you encrypt your real root or not.  You'd have to
    play with it, but I recommend reserving that 1GB for potential future
    use for things like that.

    The only real issue with SSD swap/swapcache has to do with excessive
    normal paging to swap, which can eat up the SSDs life (i.e. not even
    related to 'swapcache' itself, which is rate-limited).  /boot itself
    has virtually no impact on a SSD since it is only rarely written to. 
    Even installing a new kernel every few weeks would not have any impact.


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