Re: safe file systems
Ralf Baechle (ralf@cobaltmicro.com)
Sun, 28 Sep 1997 18:29:48 -0700 (PDT)
> Chris> I think even my cheapish SCSI disks (which have a 1 (maybe 2?)
> Chris> MB cache) will do this. I assume here a system reset will not
> Chris> affect them, but power-failure did last time I checked. (But
> Chris> you can twiddle with the tables on them and modify the way it
> Chris> writes data back, etc).
>
> Once I read (dunno where) some drives used to keep an small
> battery enough to flush all the writes from the cache to the disk in
> case of power down. Even I read on that same messages about others
> using the disk's inertia to generate power to do the flushing
> ... though this looks quite strange to me ...
A battery or a capacitor with enough energy to power a disk drive for
some seconds is relativly bulky and costs money. The rotational
energy of the spindle is for free.
One of my older disks, a 11" drive with a 4.8mb fixed and a 4.8mb medium
mounted on the same spindle contained two capacitors, each about 1l in
volume for just retracting the heads from the media to avoid a headcrash
in case of powerfailure ...
Ralf