[9fans] kfs and cwfs comparison

[9fans] kfs and cwfs comparison

[errno]

Hello!

Question, regarding kfs and cwfs: why choose one over the other?

In other words, what points are important to be aware of when deciding
which of the two are more appropriate for any given new
installation/deployment? (let's assume that kfs's 28-character filename
limit isn't an issue, and that there's no concern for supporting legacy fs
formats)

Additionally, under what conditions/circumstances might either of those
two be a more suitable/optimal alternative to, say, fossil?

Thanks!

Re: [9fans] kfs and cwfs comparison

[erik quanstrom]

> Question, regarding kfs and cwfs: why choose one over the other?
>
> In other words, what points are important to be aware of when deciding
> which of the two are more appropriate for any given new
> installation/deployment? (let's assume that kfs's 28-character filename
> limit isn't an issue, and that there's no concern for supporting legacy fs
> formats)
>
> Additionally, under what conditions/circumstances might either of those
> two be a more suitable/optimal alternative to, say, fossil?

in my experience, both are more robust in the face of unexpected outages
than fossil.

ken fs/cwfs also provides a dump file system (that is, history) without the
need to run venti.

- erik

Re: [9fans] kfs and cwfs comparison

[errno]

On Sunday, April 24, 2011 04:13:59 AM erik quanstrom wrote:
> > Question, regarding kfs and cwfs: why choose one over the other?
> >
> > In other words, what points are important to be aware of when deciding
> > which of the two are more appropriate for any given new
> > installation/deployment? (let's assume that kfs's 28-character filename
> > limit isn't an issue, and that there's no concern for supporting legacy
> > fs formats)
> >
> > Additionally, under what conditions/circumstances might either of those
> > two be a more suitable/optimal alternative to, say, fossil?
>
> in my experience, both are more robust in the face of unexpected outages
> than fossil.
>
> ken fs/cwfs also provides a dump file system (that is, history) without the
> need to run venti.
>

Thanks for the info - couple more questions, if you don't mind:

How about in terms of resources/overhead - is kfs more appropriate in
constrained/embedded devices than cwfs?

Or maintainability? Are kfs and cwfs both relatively equal in terms of
maintenance and/or disaster recovery?

Are kfs and cwfs equally dependable/stable?

Finally, what about the difference between a terminal and auth/cpu/fileserver -
would kfs/cwfs be more or less appropriate for a terminal vs. a server?

I'm curious, because I'm about to do another plan9 install after a pretty
long hiatus; and this time I'd like to switch filesystems (fossil/venti
distracted from my plan9 learning curve a bit last time) - I'd just like to
get some extra info that's not in the man pages, so that I can make a
more informed decision.

Re: [9fans] kfs and cwfs comparison

[David du Colombier]

kfs is a local and single-user file server without any archiving mechanism.

It was intended to be used on terminals with a disk and it is not aimed to be
used on a file server machine.

It is similar to the "other" file system of ken's fs or cwfs and share most of
its code with it.

--
David du Colombier

Re: [9fans] kfs and cwfs comparison

[erik quanstrom]

On Sun Apr 24 10:11:16 EDT 2011, 0intro@gmail.com wrote:
> kfs is a local and single-user file server without any archiving mechanism.

s/single-user //

it may have been at one time, but kfs does handle multiple users.
(as long as strlen(username)>1.  i'm surprised anthony hasn't complained. ☺)

- erik

Re: [9fans] kfs and cwfs comparison

[Steve Simon]

> I'd just like to
> get some extra info that's not in the man pages, so that I can make a
> more informed decision.

There are papers: /sys/doc/venti/venti.ps, /sys/doc/fossil/fossil.ps,
and /sys/doc/fs/fs.ps

There is also paqfs which is a readonly file system and a flash filesystem
which might be of interest for embedded work.

Ideally there would be a wiki page on this - I will have a go shortly...

-Steve

Re: [9fans] kfs and cwfs comparison

[erik quanstrom]

> How about in terms of resources/overhead - is kfs more appropriate in
> constrained/embedded devices than cwfs?

by default, kfs just uses 10mb of memory.  i haven't run cwfs enough to
say with any confidence how well cwfs does.  but kfs will use less disk
space (and if no changes, constant space) since old copies are not kept.

> Or maintainability? Are kfs and cwfs both relatively equal in terms of
> maintenance and/or disaster recovery?

both have a weak spot.
kfs.  there's one copy of the file system.  if you corrupt it, you're out of
luck.  i've never seen this happen.

cwfs.  if the fs is halted during the dump, there is a non-zero chance
of corruption.  i have seen this, but "recover main" can usually roll the
fs back to the last good dump.  the same mechanism can recover a fs
if an untimely shutdown has corrupted the cache.

> Are kfs and cwfs equally dependable/stable?

i would say so.

> Finally, what about the difference between a terminal and auth/cpu/fileserver -
> would kfs/cwfs be more or less appropriate for a terminal vs. a server?

it depends.  i would tend to use kfs only if i were storing my real data
someplace else.  i find the lack of history to be a big problem.  but then
again, i tend not to run fses on terminals.  i just run ken's fs and am done
with it.  :-)

- erik

Re: [9fans] kfs and cwfs comparison

[John Floren]

On Sun, Apr 24, 2011 at 9:10 AM, erik quanstrom <quanstro@quanstro.net> wrote:
> both have a weak spot.
> kfs.  there's one copy of the file system.  if you corrupt it, you're out of
> luck.  i've never seen this happen.
>
> cwfs.  if the fs is halted during the dump, there is a non-zero chance
> of corruption.  i have seen this, but "recover main" can usually roll the
> fs back to the last good dump.  the same mechanism can recover a fs
> if an untimely shutdown has corrupted the cache.
>

The other day I managed to fill up a cwfs fscache, making it
impossible to dump or boot the machine. Is it possible to recover from
this state?


John

Re: [9fans] kfs and cwfs comparison

[erik quanstrom]

On Sun Apr 24 13:37:08 EDT 2011, john@jfloren.net wrote:
> On Sun, Apr 24, 2011 at 9:10 AM, erik quanstrom <quanstro@quanstro.net> wrote:
> > both have a weak spot.
> > kfs.  there's one copy of the file system.  if you corrupt it, you're out of
> > luck.  i've never seen this happen.
> >
> > cwfs.  if the fs is halted during the dump, there is a non-zero chance
> > of corruption.  i have seen this, but "recover main" can usually roll the
> > fs back to the last good dump.  the same mechanism can recover a fs
> > if an untimely shutdown has corrupted the cache.
> >
>
> The other day I managed to fill up a cwfs fscache, making it
> impossible to dump or boot the machine. Is it possible to recover from
> this state?

recover main should flush the cache, but that's probablly not what you want.
if you're not using the fast-cache option, just make the cache device bigger.

this is a bug and should be fixed or mitigated.

- erik

Re: [9fans] kfs and cwfs comparison

[errno]

On Sunday, April 24, 2011 09:10:22 AM erik quanstrom wrote:
> <snipped>

Thanks for satisfying those questions, much appreciated!

On Sunday, April 24, 2011 08:01:01 AM Steve Simon wrote:
> Ideally there would be a wiki page on this - I will have a go shortly...
>

That would be helpful; looking through the archives, I can see
that similar questions - regarding the effective differences between
the various plan 9 disk fs's - have been brought up on the list before.



On Sunday, April 24, 2011 09:10:22 AM erik quanstrom wrote:
> > How about in terms of resources/overhead - is kfs more appropriate in
> > constrained/embedded devices than cwfs?
>
> by default, kfs just uses 10mb of memory.  i haven't run cwfs enough to
> say with any confidence how well cwfs does.  but kfs will use less disk
> space (and if no changes, constant space) since old copies are not kept.
>
> > Or maintainability? Are kfs and cwfs both relatively equal in terms of
> > maintenance and/or disaster recovery?
>
> both have a weak spot.
> kfs.  there's one copy of the file system.  if you corrupt it, you're out
> of luck.  i've never seen this happen.
>
> cwfs.  if the fs is halted during the dump, there is a non-zero chance
> of corruption.  i have seen this, but "recover main" can usually roll the
> fs back to the last good dump.  the same mechanism can recover a fs
> if an untimely shutdown has corrupted the cache.
>
> > Are kfs and cwfs equally dependable/stable?
>
> i would say so.
>
> > Finally, what about the difference between a terminal and
> > auth/cpu/fileserver - would kfs/cwfs be more or less appropriate for a
> > terminal vs. a server?
>
> it depends.  i would tend to use kfs only if i were storing my real data
> someplace else.  i find the lack of history to be a big problem.  but then
> again, i tend not to run fses on terminals.  i just run ken's fs and am
> done with it.  :-)
>
> - erik