SUMMARY : UFS Logging, pros and cons

Thanks goes to the following people. Their suggestion has helped me a lot in
making decision whether or not I should implement UFS logging in my all boxes.
Please see their great suggestions below:

Thanks!
Amindra





There is a slight (around 5%) performance hit with UFS logging.  For
most environments (ours being one; we use UFS logging everywhere), the
consistency benefits outweigh the performance hit.  For most, not for all.
HTH...

Kevin Buterbaugh
LifeWay

================================================================
Ive never seen any mention or have experienced any cons with ufs logging.

Steve Mickeler


===============================================================
Amindra,

> In recent past I found summary for ufs logging option.

Glad to see you caught up.

> My question is why people don't use it all the times. This is a good
feature
> and we should make it mendatory in our world.

Good question. Put another way, why isn't in on by default?

> Is there any performance issue or any concern why we should not use
> logging?

I have yet to hear of any real or convincing theoretical situation in
which logging would be in any way harmful. It appears to be that rare
quality - no downside.


-Andrew-
===============================================================

I run logging on *all* my ufs file systems (except as I mention in 2
below).

Reasons to not run logging:

1)  I'm told by people I trust that there are *some* circumstances
    where logging is slower than nologging.  In my applications, I've
    always found logging to actually be faster, but there's all
    sorts of applictions out there, right?

2)  If I'm restoring an entire file system (or large fraction of
    a large file system), I turn logging off, and use fastfs
    (http://www.science.uva.nl/pub/solaris/fastfs.c.gz).

    But *only* until the ufsrestore/tar is done.  Then fastfs back
    to slow mode, and logging back on.

--
Jay Lessert


===============================================================
My understanding is that there are a few usage patterns where UFS
logging really hurts performance and that is why Sun has not yet
made it the default.  I have it turned on on all of our Sun boxes
here and love it.

Jason


===============================================================
Mainly because they don't know about it.  I believe logging is on by default
in Solaris 9.

Logging can, in one or two very specific cases, cause a performance hit, but
most of these cases are things which will not happen in general use. In
almost all cases logging will increase performance.
You also loose about 1Mb/Gb of disks space with logging on.

  Scott.



===============================================================
I had one bad experiance. A E420 setup by a sun engineer had logging turned
on for /, /var and other key OS filesystems. Somehow /var (no one knows
how) became corrupt and the system paniced. The system would not check
the file systems when it rebooted itself and therefore kept panicing and
rebooting. Because I didnt know about "boot -b" I had a hard time fixing
it.

So my policy on this is not to have logging turned on for OS filesystems.
They are going to be small enought that a fsck wont take too long. I would
use it for large user file systems (but Im now using veritas for these)

BB

===============================================================
I use logging wherever possible. The pros do indeed outweigh the cons.
There is a performance impact, though. Also note that with DiskSuite you
can put the log on a different device, which may improve performance if
you do it right.

If you don't need to keep track of last file access times, you may want to
mount partitions with the noatime option. This will suppress a lot of
metadata
updates which generate log traffic.

system administration account sysadmin@astro.su.se

Original question:

Hi Admins,

In recent past I found summary for ufs logging option. We can use logging
option in /etc/vfstab and we can remount the existinf mounted ufs file system
using logging option. I found its very good because the system doesn't need to
run fsck during the boot even if the system was shutdown abruptly.

My question is why people don't use it all the times. This is a good feature
and we should make it mendatory in our world. Is there any performance issue
or any concern why we should not use logging? Any information is greatly
appreciated.

Best regards,
Amindra
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