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Boot some MacBook Pros via an ExpressCard solid state drive
Authored by: bkr on Dec 17, '09 12:11:29PM

Be careful what you buy.
The FileMate is the only one which is bootable - according to my research
with distributors and users. The Verbatim (which has wider distribution) requires
a driver even for normal operation.
The FileMate registers in the system as a SATA controller - I think this is the key.
I use it for the same reasons as the original poster but with a few
modifications:
I have a launchd item which fires up a 1.5G ram disk (the MPB has 6G) mounted at
/private/var/folders - the reason for the weird mountpoint being
a leftover of trying to do it very early.
I have also symlinked some directories (/private/var/log, ~/Library/Caches and Logs)
to the ram disk because I wanted to remove as many write operations as possible since
this is what brings up the heat (and the wear).
There are reasons to call me stupid for using a ram-disk but see below.
/private/var/vm is symlinked to the hard disk.
In my (coarse) measurements using the ioreg tool I found that the SSD consumes
about as much (120mA) as an idling 5400rpm Seagate - this is not much compared
to the backlight, so I don't mind if both are running.
The problem with the ram disk approach is that the system won't shut down because
it can't unmount the ram disk while daemons have files open there.
This asks for further tinkering which I will do when I am bored enough :-)
Right now I wait a few seconds and squeeze the power button.
The perfect thing IMHO would be to make the ramdisk the system root,
populated from a disk image like many
linux-install setups do (initrd). I found very little information about this stuff,
the kernel code has some hooks but in my short research I didn't find anything usable.
In my opinion, this SSD is recommendable if either you don't care about a bit of heat
or you don't mind some serious tinkering with your system.
For me, it will stay because of the combination of blazingly fast app startup and a 500G disk.
I am under the impression that it pays to have /private/var/folders (where most temp files go)
on a ram disk - if your usage scenario does not involve very big temp files.



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