THANKS TO :
Alan Rollow : alan_at_nabeth.cxo.dec.com
Tim Mooney : mooney_at_toons.cc.ndsu.NoDak.edu
SUMMARY : On-line backup, Advfs and swap
Basically, the injunction in the manual about having advfs file
domains on partition c may be optimal in theory, but in practice
advfs should be treated the same as any other file system. For those
wanting root and /usr on the same disk (I suspect that is most of us)
the Advanced installation does the OPPOSITE of what the manual
recommends, putting root and /usr in separate file domains on the
same disk, rather than as separate filesets within the one domain !!!
FOLLOW-ON QUESTIONS :
1) Is there a good reason why the Advanced installation creates
separate file domains for root and /usr on the same disk, contrary
to the advice in the manual ? If so, what is that reason ?
2) How does Networker save & restore handle open files ? Does it
ignore them, save them in a possibly inconsistent state, or is it
=really= clever ?
ANSWER FROM alan_at_nabeth.cxo.dec.com :
I suspect that the "whole disk" recommendation is simply
to allow whatever file system is on it to not have to
complete for disk accesses. The same recommendation
applies to any disk, if you want the file system on it
to have the best performance. I don't if there is anything
that AdvFS that makes this arrangement more desirable than
for other file system.
The installation procedures offers the ability to chose
AdvFS when the system is first installed. It will create
a different domain for each of the three file systems
offered at installation; /, /usr and /var. I'm not entirely
sure why it does this, but if there's a good reason, you'd
probably do well to arrange yours the same way.
The typically installation will put root on A (32-64 MB)
page/swap on B (128 MB), /usr on the next largest partition
(usually G or H) and will offer the option of putting /var
on whatever is left. In your case you'd probably want to
create /usr/users on whatever is left and keep /var on
/usr.
If paging and swapping ever becomes a consideration, spreading
the page/swap across multiple disks can improve the performance
some. So, putting some page/swap space on the 2nd drive is
a good idea. If the paging I/O is enough to cause problems
for whatever file system is on the 2nd disk, then you have
a more serious performance problem than a slow file system.
I would partition the 2nd drive as A, B and some partition
for all the left over space. You can use A as a backup copy
of the root (or see if you can use it as a mirror with LSM).
Or, depending on the load put /tmp there. Use B for the
secondary page/swap and the remaining partition for whatever
application needs the space or as an extra volume in the
domain for /usr/users.
ANSWER FROM : mooney_at_dogbert.cc.ndsu.NoDak.edu
I use both LSM and AdvFS on several machines, and
Networker has no problems with either.
>Another possibility is Advfs, clone file sets and vdump, which
>may have additional advantages such as quicker boot times.
We use that method on another machine that isn't currently
licensed for Networker, and it works fine (though restores are
nowhere near as pleasant as with Networker).
>Things I've read suggest the news spool disk should be set up
>using ufs, so I guess Advfs is a possibility only for the first
>drive.
That depends on the size of your news spool, but it is true that
a lot of people have run into problems with using AdvFS as the
fs on the news spool. Most of those problems have been for
people that run out of metadata. There are suggestions in the
archive for this mailing list on how to prevent this problem
when the file domain is created.
>My reading of the SysAdmin manual ch8 suggests that for
>performance reasons, an Advfs file domain should occupy a whole
>drive, ie partition c. How then can you provide swap space ?
I'm not sure what the right answer is here, but I think the
manual just means that (obviously) you should avoid contention
by not putting too many file domains on one disk.
>What about setting up a 1.9GB partition 'a' and a 100 MB
>partition 'b', and having 'a' be a file domain with three
>filesets : root, /usr and /usr/users. 'b' becomes swap1. Is
>this a good idea or a bad idea ? Clearly it contravenes the
>suggestion for optimum perfomance in the manual.
I think the manual may not be stating the goal in the best
terms. What you probably want to avoid, if you're really
worried that your server is going to be loaded, is having more
than one file domain on the same disk. You should be fine using
*almost all* of the disk for one file domain and then using a
small amount for something else. I suspect the manual is just
warning against having a disk with several file domains on it.
>Another idea is to put all the swap on the second drive, which
>is not optimal for swap performance, and has the further
>downside that if the second drive goes down, the whole system
>becomes inoperable because of lack of swap space. Is this
>preferable to the scenario above, or not ?
I'm pretty sure the install process won't permit you to put
swap1 anywhere other than on the drive that contains your /
filesystem. I suppose you could undo this after the install,
but it doesn't seem like a good idea.
__________________________________________________________
Martyn Brown, Snr Computer Consultant, ph 64 3 3252 811
Computer Services, Lincoln University, fax 64 3 3253 865
Canterbury, New Zealand email brown_at_lincoln.ac.nz
Received on Thu Jul 04 1996 - 23:51:36 NZST