URGENT: Disk Performance Issue

URGENT: Disk Performance Issue

Post by Subhankar Pand » Fri, 13 Nov 1998 04:00:00



Hi All,
I have got a VAX 3100 system with RF73 type of disk.

I found deletion of 500 files takes approximately 10 mins.
I checked the error log, no entries were found, except logs during mounting with 0 errors.
I am unable to find any reason for the same. Just give me the probable reasons.
Please help.

Thanking you in advance,

Regards,

S. Panda

 
 
 

URGENT: Disk Performance Issue

Post by Jan Vorbruegge » Fri, 13 Nov 1998 04:00:00



> I found deletion of 500 files takes approximately 10 mins.

Is the directory containing those files larger than 127 blocks? That seems the
most likely explanation.

        Jan

 
 
 

URGENT: Disk Performance Issue

Post by Bart Z. Lederm » Fri, 13 Nov 1998 04:00:00



>Hi All,
>I have got a VAX 3100 system with RF73 type of disk.

>I found deletion of 500 files takes approximately 10 mins.
>I checked the error log, no entries were found, except logs during mounting with 0 errors.
>I am unable to find any reason for the same. Just give me the probable reasons.
>Please help.

It's really not going to be possible to answer this question
without a lot of additional information: such as, how large
were the files, were they all in one directory, did they
all have similar names, how was the disk set up, and
most important of all, what else was the system being used
for at the time?  Also, what model of 3100 is it, how much
memory do you have, and how much is free / what software
is loaded?

Assuming that the system was tuned properly, that it was
operating properly, that there was not a lot of other
activity on the system at the time, and that there was
nothing 'wrong' with the directory structure or file
names: then the most likely cause is that they were
very large files and you have the disk set for erase
on delete.  This is going to take a while, especially
on a low-end VAX 3100, as it uses a fair amount of CPU.

But there are a LOT of 'ifs' in this guess.

--
 B. Z. Lederman   Personal Opinions Only

 Posting to a News group does NOT give anyone permission
 to send me advertising by E-mail or put me on a mailing
 list of any kind.

 Please remove the "DISABLE-JUNK-EMAIL" if you have a
 legitimate reason to E-mail a response to this post.

 
 
 

URGENT: Disk Performance Issue

Post by Hoff Hoffm » Fri, 13 Nov 1998 04:00:00


  Urgent requests should use the formal software support channels
  available to you -- this could be local support, or the Compaq
  customer support center.

:I have got a VAX 3100 system with RF73 type of disk.

  You will want to specifically identify the system type, as the
  most typical members of the "3100" series -- the MicroVAX 3100
  and VAXstation 3100 -- do not support DSSI connections necessary
  for the RF73 disk.

  You will also want to identify the OpenVMS VAX version.

:I found deletion of 500 files takes approximately 10 mins.
:I checked the error log, no entries were found, except logs during mounting
:with 0 errors. I am unable to find any reason for the same. Just give me the
:probable reasons.

  For the deletions taking so long?  (The note is somewhat ambiguous,
  I will assume that this was a deliberate DELETE operation, and that
  the question is one of performance.  I will assume that this is not
  a question of tracking down the cause of a mysterious deletion of
  500 files.)

  Performance problems are often extremely difficult to resolve via
  newsgroup postings -- these problems often require large amounts of
  contextual, historic, and configuration information to resolve...

  Look for disk fragmentation, excessively low process quotas, low
  system resources, insufficient pagefile space, competing traffic
  on the same disk spindle, DSSI or bus contention, etc.  Use the
  techniques called out in the performance management manual to try
  to track down the specific system performance problems.

 -------------------------- pure personal opinion ---------------------------

  note to those folks not contributing spam -- there is no ZZ in my address

 
 
 

URGENT: Disk Performance Issue

Post by gr.. » Fri, 13 Nov 1998 04:00:00




>> I found deletion of 500 files takes approximately 10 mins.

> Is the directory containing those files larger than 127 blocks? That seems the
> most likely explanation.

>    Jan

And if that isn't the problem, it is possible that the files are large
and the disk volume is set to "erase on delete".
 
 
 

URGENT: Disk Performance Issue

Post by Subhankar Pand » Sat, 14 Nov 1998 04:00:00


Hi,
No volume is not enabled with flag ERASE_ON_DELETE nor HIGH_WATER_MARKS set.
Also, the DELETE command does not contain /ERASE qualifier.

Thanking you,

Regards,

Subhankar

*************************************************************************
Subhankar Panda
ENS-FRS9000
Hughes Software Systems
Plot 31, Electronics City
Sector 18, Gurgaon - 122015
Haryana, India
Phone: +91 124 346666, 343703-343707 ext 2318/2124
Fax: +91 124 343723

*************************************************************************

-----Original Message-----

Sent:   Thursday, November 12, 1998 10:54 PM

Subject:        Re: URGENT: Disk Performance Issue



>> I found deletion of 500 files takes approximately 10 mins.

> Is the directory containing those files larger than 127 blocks? That seems the
> most likely explanation.

>    Jan

And if that isn't the problem, it is possible that the files are large
and the disk volume is set to "erase on delete".

 
 
 

URGENT: Disk Performance Issue

Post by Carl Perki » Sat, 14 Nov 1998 04:00:00



}Hi All,
}I have got a VAX 3100 system with RF73 type of disk.
}
}I found deletion of 500 files takes approximately 10 mins.
}I checked the error log, no entries were found, except logs during mounting with 0 errors.
}I am unable to find any reason for the same. Just give me the probable reasons.
}Please help.
}
}S. Panda

The most probable reason is that they were all in the same directory and the
diretory file was most then 127 blocks in size.

When a directory file is bigger than that, it is not cached. Directory files
are not allowed to have empty blocks, so when all info in a block is deleted
the data in the rest gets shifted towards the front of the file.  A wildcard
delete processes the files in alphabetical order and files are stored in the
directory file in alphabetical order.  Combine all of these bits of info and
the result is that deleting a large number of files using the easiest method
is often very slow.

The DFU utility, avialble in various places like the VMS Freeware CD, may be
useful for speeding this up, as might a simple DCL proceedure to do the file
deletions in reverse alphabetical order. Other things could help, it depends
on exactly what you were doing (and how accurate my guess is).

--- Carl

 
 
 

URGENT: Disk Performance Issue

Post by Charlie Hammo » Sat, 14 Nov 1998 04:00:00



Quote:> I found deletion of 500 files takes approximately 10 mins.

The time to delete a large number of files in a single directory can
often be decreased by deleting the files in reverse alphabetical order.
This can be done by writing a DIRECTORY command output to disk; sorting
the disk file; and then reading it in to a DCL procedure.

The time to create a large number of files in a single directory can
often be decreased by deleting the files in reverse alphabetical order.
I have no general solution on how to accomplish this.

The reason for this is that this ordering reduces the amount of re-writing
that needs to be done to the directory file.

In truely pathological cases this ordering can decrease processing time
from hours or even days (honest!) to minutes.  

Whether the case in question can be inprooved and by how much can only
be determined by experimentation. (i.e. TRY it.)

Other things to check:

    - Is the process doing the the delete getting enough CPU time?
      Or is it at a low priority in a system with high CPU usage?

    - Is there a lot of other I/O going on to this disk?

Depending on many things, deleting files at the rate of nearly one per
second isn't that bad.

--
    Charlie Hammond -- Compaq Computer Corporation -- Pompano Beach  FL USA

      All opinions expressed are my own and not necessarily my employer's.

 
 
 

URGENT: Disk Performance Issue

Post by Stephen Davi » Mon, 16 Nov 1998 04:00:00


This is fixed in V7.2.

This is caused by the way VMS creates a file list and then deletes the files
one at a time. Moving the disk head to and fro
while updating the directory entries one at a time.  This is NOT a disk
performance problem, rather a current feature of
the OS. Meaning, it was coded to do exactly what you are experiencing.  Some
of the workarounds listed in this message thread may help your specific
situation.

VMS V7.2 scheduled for release in March '99 ( subject to change, of course)
has a coding change to perform multiple
deletes much more quickly...

Steve
Compaq (formerly Digital)

 
 
 

URGENT: Disk Performance Issue

Post by Paul Repachol » Sat, 21 Nov 1998 04:00:00


If you need to delete lots of files,

backup/delete/nocrc/group=0 victim nla0:./sav

You MUST include the dot...

Or. if you have it, use DFU without SMG mode

~paul

 
 
 

1. Apostrophes. Was: Performance problem (Urgent)



Hear, hear!

Well said Hoff, that hacks me off too!

(as does people typing "here here" when they agree with something, I suppose
in an email, it should be "Read, read!")
=====  wants Windows NT v8.0 to be!"  (Compaq, 22-Sep-1998)

Systems Programmer, Synergex; 2330 Gold Meadow Way;
Gold River, CA 95670 Phone: 916/853 0366; http://www.synergex.com


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