My thanks to:
dritchey_at_cecc.chi.gov
rockwell_at_rch.dec.com
alan_at_nabeth.cxo.dec.com
In summary - Advfs will stripe a specific file, lsm will allow you to setup a
file system that stripes across multiple disks. I blew away the advfs volume
and created a filesystem that was striped across the three rz29b's.
Jim
>From dritchey_at_cecc.chi.govWed Nov 15 16:42:58 1995
> I'm new to the list and have seen some discussion lately on not using an
> advfs stripe set as my news spool. Thanks to Hugh Messenger for pointing
> me to the archive and to Barry Lyman for a great rundown on his trials
> and tribulations with this set up. I've got a couple of questions that I
> still am a little vague on. As to setup, the machine is 2000 4/166 with
> 3 rz29b's for spool. I currently have them striped with advfs.
>
> 1. What's the difference between using ADVFS and LSM to stripe disks?
As I understand it, ADVFS stripes files, so unless your files are fairly static
and rather large, it really isn't worth it.
LSM, on the other hand, stripes file systems, where the striping is performed
at the file system block mapping level. This means that blocks 0 - (n-1) are
on disk 1, blocks n - (2n-1) are on disk 2, etc. This is a performance
advantage for all files in the file system, not just the individual files that
ADVFS lets you strip.
> 2. If I heed Alan Rollow's advice and defragment daily, am I pretty safe
> in using striping thru advfs?
The advice I got from Digital customer support was to use LSM for basic
striping and performance reasons, then use ADVFS for fast recovery from system
panics or the like. (We are doing heavy duty development and some of the
really hairy system problems result in kernel panics, with ADVFS we are up and
running in about three minutes, without ADVFS, the fsck of all the file systems
can take 15 minutes or more.)
Questions?
>From rockwell_at_rch.dec.comWed Nov 15 16:43:09 1995
> 1. What's the difference between using ADVFS and LSM to stripe disks?
AdvFS striping stripes individual files across the volumes of a multiple
volume AdvFS domain.
You have to manually set up each file that you want to stripe (create it first, tell AdvFS to stripe it, then you can write into it and it'll be striped across each volume.
AdvFS striping is not a practical thing for a news spool where you have files
created and deleted on a constant basis.
LSM striping stripes a whole logical volume across multiple subdisks
(or partitions). If you build a striped volume out of, say 3 2GB disks,
anything written to the volume will be striped across the 3 disks. So, if
you use this logical volume in an AdvFS domain, anything written to that
volume will be striped automatically.
Gotchas:
You can't extend an AdvFS domain by extending a LSM volume. You extend an
AdvFS domain by adding new volumes (logical or physical). So if you want
this new extension to be striped, you should build a striped LSM logical
volume, then add it to the AdvFS domain.
>
> 2. If I heed Alan Rollow's advice and defragment daily, am I pretty safe
> in using striping thru advfs?
Striping isn't the issue. It's AdvFS behavior with many files that are
created and deleted (like news spools) that causes the problems. You'll
find the same AdvFS issues whether you use LSM striped volumes or not.
>From alan_at_nabeth.cxo.dec.comWed Nov 15 16:43:20 1995
The main difference between using Advfs to stripe and using
LSM is that Advfs can only stripe individual file, where LSM
can stripe the entire volume. So, if you want large news
files striped using Advfs, you would have to create a new
file, stripe it, copy the old file to the new one, delete
the old one and rename it. There's currently no way to get
all files striped.
With LSM you create a stripe of the underlying disks and hand
that off to the file system that will use them. UFS is the
better choice for News, since Advfs has problems with News
like I/O loads.
Received on Thu Nov 16 1995 - 17:17:23 NZDT