27 Feb
2021
27 Feb
'21
2:54 p.m.
Hi Larry et al,
Just curious about this: was there any feedback from Jeff Bonwick and/or
Bill Moore re the ARC -vs- page cache?
Or would any of the design notes document the reasoning behind the decision?
Surely it must have come up and been justified or got an exception in the
Solaris architecture review (SARC "20 Q's", wasn't it called?) Since
AFAICS
it affected Solaris O/S interface (former-)guarantees. Although those notes
are probably lost / inaccessible now...
There's also the monthly OpenZFS leadership meeting, Matt Ahrens et al are
in there: I wonder if they would have access to some of the original
reasoning; how it was justified / why it was permitted.
Dave, btw: check out the high-level structure of ZFS metadata -- every
block is checksummed, and the checksum kept in the parent block (i.e. *not*
kept together), applicable for both data and metadata blocks, and at least
two copies are kept of metadata (but you can request more depending on your
paranoia, see also "ditto" blocks). Compression is optional at the
filesystem level (not held at the pool aka volume level; a pool may contain
multiple filesystems), when compression is enabled if affects future
created files, same if unset or changed to another algorithm; the
filesystem handles a mix of files (blocks, even; I forget offhand) existing
with various or no compression.
Rgds, Stuart.
On Sat, 6 Feb 2021 at 10:56, Larry McVoy <lm(a)mcvoy.com> wrote:
On Fri, Feb 05, 2021 at 06:22:32PM -0800, Rico
Pajarola wrote:
sets
On Fri, Feb 5, 2021 at 12:51 PM Dave Horsfall
<dave(a)horsfall.org> wrote:
> Thanks; I'd heard that ZFS was a compressed file system, so I stopped
> right there (I had lots of experience in recovering from corrupted
RK05s,
and
didn't need any more trouble).
That's funny, for me this is the main reason to use ZFS... What really ZFS apart from everything else is the lack of
trouble and its resilience
to
failures.
I'm gonna call Bill tomorrow and get his take again, that's Bill Moore
one of the two main guys who did ZFS.
This whole thread is sort of silly. There are the users of ZFS who love
it for what it does for them. I have no argument with them. Then there
are the much smaller, depressingly so, group of people who care about OS
design that think ZFS took a step backwards.
I think Dennis might have stepped in here, if he was still with us, and
had some words.
I think Dennis would have brought us back to lets talk about the kernel
and what is right. ZFS is useful, no doubt, but it is not right from
a kernel guy's point of view.
I miss Dennis.