On Tue, 30 Apr 1996 06:25:36 +0000 (GMT), kris @
>There are several options to beat the metadata update
>bottleneck. [AIX JFS, Osterhout's LFS]
Another option is a non-volatile disk cache: Once the data gets into
the cache, it doesn't matter if you lose power. Sun's PrestoServe is
one example of such a product. It's an S-bus card (or some special
SIMM modules for the newer SPARCstations) plus software that caches
all synchronous disk writes. Sun sell it as an NFS accelerator (since
NFS writes are synchronous by definition) but it also really helps
things like 'rm -fr /' :-).
One area that hasn't been mentioned so far is what happens when power
goes away whilst the disk is in the middle of a write. Or for that
matter, what happens to the data in the disk drives internal cache
when power is lost. Luckily, most disk manufacturers seem to have
stopped implementing the `retract heads whilst writing' feature that
did the most damage. This is one area where proper power supply design
(and proper disk design) could impact filesystem reliability.
Peter Jeremy (VK2PJ) peter .
Alcatel Australia Limited
41 Mandible St Phone: +61 2 690 5019
ALEXANDRIA NSW 2015 Fax: +61 2 690 5247
PGP fingerprint: 2A C6 47 D1 BF 56 5A 10 CC 02 2D 89 EA 10 AA 40