Re: safe file systems
Darren Reed (darrenr@cyber.com.au)
Thu, 25 Sep 1997 08:33:32 +1000 (EST)
In some mail I received from Larry McVoy, sie wrote
>
> : [write re-ording]
> :
> : I think even my cheapish SCSI disks (which have a 1 (maybe 2?) MB cache)
> : will do this. I assume here a system reset will not affect them, but
> : power-failure did last time I checked. (But you can twiddle with the tables
> : on them and modify the way it writes data back, etc).
>
> The default on every SCSI & FC disk I've ever seen (and I've seen a
> fair number including drives from HP, Seagate, Quantum, IBM, Maxstor,
> and probably others I'm forgetting) is to /not/ do write caching. If
> the drive says the write is done, it is done.
>
> You can, as you mentioned, change this behavior, but the default as shipped
> from the vender is that it does not do write caching.
>
> And no work station vendor (Sun/SGI/HP) that I know of turns them on - it
> would be highly unreasoable to do so.
Hmmm, according to what I've been told, HP used to ship drives with their
own firmware to guarantee writes would be done if there wa a power failure.
This was for their older F & G series boxes which had a bettery in them to
keep RAM & disk `alive' (but not running) in the case of a power failure
for ~10-15 minutes - this is NOT a UPS simulator. I don't know if they
also made use fo the cache for writing.
Darren