Hello,
I'd like to send this to all of you those few lines. This was my private
correspondece with Mr. Thomas Blinn, <tpb_at_zk3.dec.com>. I believe he
won't mind if I make few of HIS OWN words more public. It's continuation
of discussion on this list about slow performance of NNTP servers,
differences between filesystems, how to oraganize your partitions, what
filesystem to choose for what. It definitely helped out the dark, and was
good intro to DUnix ;-) while I was installing 4.0D.
> Tom,
> I've read some SUMMARY of someone on the list and I'd like to ask you again:
> Why I shouldn't use AdvFS on #root domain?
>
> I have root domain (of course one volume!), but the volume is AdvFS. I
> know it's stupid to add another volume to this domain. Before I install
> the 4.0D on the system, I can switch to UFS for /. But, isn't AdvFS
> safer(if contains only 1 volume)?
>
> BTW: Is UFS faster than AdvFS? Or why do some people use UFS for NNTP
> servers? We started running proxy cache, well, the perfoirmance went down.
> The processor is idle 60% or more, but disks i/o are slow. What would you
> recommend me?
>
> TIA
> Martin
The *only* thing that AdvFS buys for you on a typical root file system is
that if your system panics or loses power, when you reboot, if there were
any file system metadata changes in progress on the root file system, then
the AdvFS log gets replayed, and maybe, if you are lucky, you wind up with
a completely valid file system structure. UFS provides the same thing, and
provides the added assurance that you've actually VERIFIED the file system
metadata. It is nearly impossible to run the AdvFS verify utility on your
root file system, since the file system you are going to verify must have
ALL of its filesets unmounted to run AdvFS verify, and it's really hard to
unmount the root fileset.
When AdvFS was added to DIGITAL UNIX, you could not install a system with an
AdvFS root partition, and it was some time before that became possible. So
you can bet that there is LOTS more experience with UFS as root than with
AdvFS as root. (We do now routinely do installation tests both ways.) And
we run with AdvFS root file systems on some of our production systems, but I
don't know if we've converted them all.
If you move the /tmp file system to a separate partition (always a good idea
anyway), then there won't be much changing in the typical root file system,
and then you get a quick fsck almost every time.
Some people use UFS for NNTP servers because AdvFS doesn't handle small
files very well. It's relatively easy to badly fragment an AdvFS file
system to the point where you can no longer allocate any files on it, even
though there may be lots of free space. And prior to V4.0D, you needed a
separate AdvFS utilities license to use the defragment utility, and when we
put the defragment utility into the base in V4.0D, we found out about the
AdvFS bugs that were in the product from earlier releases that could lead to
catastrophic file system corruption (blowing away the file system and making
the system panic in the process). We *think* we fixed them all, but we were
in the last days of the release cycle when we found the last "fixes" and if
you wanted me to promise they are 100% fixed, I'd refuse.
AdvFS is a thing of beauty for some environments, but if you consider the
number of system years of use it has, compared to UFS, it's an infant. I
have yet to see evidence that it really works better for the root fs, and I
am skeptical of its benefits for the /usr file system (unless you leave the
/var file system in /usr). But it's a judgement call, you really have to
make your own choice.
It still comes down to whether there are real measurable benefits from an
AdvFS root file system, and I personally have never seen a compelling case
for them.
Needless to say, this isn't an official Digital Equipment Corporation
position on the matter, just my experience and opinion.
Tom
------------
And addendum:
> What about:
> ------
> UFS
> / 160 MB
Seems like a reasonable size to me. Should be big enough for most future
expansion.
> ------
> AdvFS or UFS (*what would you choose?*) - or even to divide it into
> separate /tmp and /var?
>
> /var (/tmp would be a link to /var/tmp)
You can't have that and get it to work reliably if you boot to single user
mode. /tmp has to be a directory or a mount point for a directory, if you
make it a symbolic link to a non-existent directory, things fail; of course
if /var/tmp exists in single user mode, you'll be OK :^)
> this is my current stage i kB:
> 281889 /usr/var/spool/mail
> 178022 /usr/var/nsr
> 723437 /usr/var
>
> ------
> UFS
> /usr/local (will be exported over AFS)
Seems reasonable.
> ------
> AdvFS
> the remaining space for /usr and swap partition.
You have to have swap be in a partition, it can't share space with a UFS or
AdvFS file system.
> BTW: Can I use the "b" partition instead of swap for data? At least
> temporarily...?
UNIX doesn't really care what you do with any particular partition. It does
not usually make sense to put two partitions on the same disk into the same
AdvFS domain, for example, because you just defeat the head movement logic
in the disk driver.
> Is there a defragment utility for UFS? Or is it so good that it doesn't
> need any?
The best defragment utility for a UFS file system is "tar" or "cpio". Just
back it up to tape or directly to another disk, if to tape then recreate it
and restore it, and the restored copy (or copy to another disk) will be as
well organized as a UFS file system ever gets. UFS is optimized for lots of
small files; AdvFS isn't, really.
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| Martin MOKREJS - Net&SysAdmin |
| PGP 5.0i key at: finger://mail.natur.cuni.cz/mmokrejs |
| mmokrejs_at_natur.cuni.cz Faculty of Science, The Charles University |
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Received on Fri Feb 20 1998 - 19:03:14 NZDT