Anyone have a guide to SSDs?

Matthew Dillon dillon at
Fri Apr 12 17:17:18 PDT 2013

:I'm getting ready to buy the box to replace the router. It will have an SSD 
:and an HDD. There's a page explaining how to put swapcache on an SSD, but do I 
:need swapcache? Which filesystems should go on the SSD and which on the HDD?

    swapcache is most useful when the machine in question is accessing
    a large data set, such as when running a large web site or handling
    mailboxes or acting as your LAN backup box for other machines.

    The main issue you have to decide upon first is whether you want to
    boot from the SSD or boot from the HDD.

    If you do want to boot from the SSD it's still possible to put swap
    on it as well, but if the SSD is small you would only want to
    configure minimal swap space (i.e. enough to cover the RAM for
    crash dumps and such, and to help back tmpfs mounts for /tmp and

    For example, I am booting one of my test boxes from one of my
    original old 40G Intel SSDs.  I have it partitioned:

	a:	1G	/boot as per normal, just on the SSD.
	b:	16G	swap (it has 16G of ram)
	d:	23G	all-in-one root filesystem (HAMMER even though
			23G is below the recommended minimum for HAMMER).

    The machine also has a HDD which I mount as /build.  And I put
    disk-eating subdirectories on /build as well, such as /usr/obj.
    e.g. /build/usr.obj and then my /etc/fstab does a NULLFS mount
    from /build/usr.obj to /usr/obj so source code builds don't
    eat space on the SSD.

    I like this setup and I think it would work very well for a
    router too by doing the /build mount from /etc/rc.local instead
    of auto-mounting it, so if the HDD dies the machine can still
    boot into a usable state and at least be able perform its routing
    functions even if it can't run other more involved services that
    you depend on data in the HDD to support.

					Matthew Dillon 
					<dillon at>

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