Re: Hard Disk Performance <-- Thanks Bela! You solved my problem(s) too!

Jerry_at_Trick
Date: 05/19/04 

Date: Wed, 19 May 2004 07:31:21 -0500

On Wed, 19 May 2004 11:54:27 GMT, Bela Lubkin <belal@sco.com> wrote:

>IanC wrote:
>
>> We have about 250 SCO Openserver installations around the UK. All of the
>> installations run Openserver 5.0.2 on a variety of 'low spec' single CPU
>> PC's with IDE disks. The specs range from a 1998 266MHz Pentium with 2Gbyte
>> disk up to 1009MHz Pentium with 20Gbyte disk.
>>
>> Some of the installations are taking much longer than others to run disk
>> intensive jobs.
>>
>> Every night each system does a backup to a single disk file (Using Backup
>> Edge from Microlite). The single disk file is then copied to tape. We have
>> used the time taken to perform the backup to disk as a measure of the
>> systems disk performance. A typical backup size is 800Mbytes of data which
>> is compressed into a single backup file of 250Mbytes.
>>
>> Our problem is that some sites take as little as 5 minutes to perform the
>> disk backup whilst others take over an hour. It is NOT the speed of the
>> processor or the spec of the disk drive which determines how long the
>> process take. Some older machines perform very well and some modern ones
>> perform badly.
>>
>> We have taken two systems with a similar spec. One takes 10 minutes to
>> perform the backup. One take 30 minutes. We find that they have different
>> types of hard disk drive. (One is a 40Gbyte Western Digital and the other a
>> 40GByte Samsung) If we swap the hard disk drive then the backup times move
>> with the hard disk. We have tried installing Linux on these two systems and
>> the backup times under Linux are fast on both machines - (6 minutes)
>>
>> We have deduced that this may be some sort of driver problem which would be
>> solved by installing a new SCO disk driver (rather than the old one which is
>> in 5.0.2)
>>
>> Has anybody got any thoughts on this and can anybody tell me if it is
>> possible to install the latest disk drivers onto 5.0.2. On the SCO web site
>> driver packages are only available for 5.0.6 and 5.0.7
>
>The "wd" IDE driver in OSR502 has no DMA support at all. All IDE I/O is
>done with programmed I/O (PIO). The driver does not attempt to control
>the PIO mode; it relies on the BIOS to have set the drive to a sensible
>mode.
>
>Take one of the systems where you noticed a big speed difference between
>two similar-spec drives. With one drive in the system, go into BIOS
>setup and see if it shows you anything about the chosen PIO mode. Many
>(but not all) BIOSes offer choices like "auto" and "PIO0-PIO4". The
>BIOS will likely be set to "auto". Hopefully it will then show what PIO
>mode it has automatically chosen. Assuming the BIOS is cooperative (by
>showing what it's done) -- you will probably be able to see that it's
>chosen different modes for the two drives.
>
>Next, read the drives' manuals and check what PIO modes they actually
>support. 40GB drives will be fairly new and _probably_ support PIO mode
>4, but it's best to check.
>
>Assuming the BIOS allows you to manually override, tell it to use the
>highest mode that the drive and BIOS both support. (The BIOS may top
>out at PIO mode 3, for instance -- either because it was written before
>PIO mode 4 was invented, or because it knows the hardware can't handle
>that.)
>
>The modes may be presented differently by the BIOS. Some use mode
>numbers, others use speeds. The modes are:
>
> PIO mode 0 3.33 MB/sec
> PIO mode 1 5.22 MB/sec
> PIO mode 2 8.33 MB/sec
> PIO mode 3 11.11 MB/sec
> PIO mode 4 16.67 MB/sec
>
>=============================================================================
>
>The current (OSR507+) version of the "wd" driver supports Ultra DMA
>modes up to 133 MB/sec. If you could use it, it would probably make a
>substantial performance difference compared to the PIO-only OSR502
>driver.
>
>The current "wd" will not link into an OSR502 kernel, but the
>incompatibility is very small, easily worked around. I have tested
>_linking_ an OSR502 kernel with the current driver and the following
>workaround. I have _not_ booted the machine (it isn't mine to boot). I
>think it will work, but if you attempt this you should first make sure
>you have good backups and crash recovery disks, be prepared for a
>potential crash.
>
>If it passes the "smoke test" and boots successfully, it's probably fine
>-- I would expect a pretty immediate failure if there's a problem.
>
>The workaround: well, first install the "Wd Driver Supplement" from
>ftp://ftp.sco.com/pub/openserver5/drivers/OSR507/btld/wdsupp/. Do not
>use the BTLD from ../wd; it won't work on OSR502.
>
>Once the supplement is installed, if you try to relink the kernel, it
>will fail with a missing symbol "swab". To correct that, edit
>/etc/conf/pack.d/wd/space.c. Find "#if !defined(MODESELECT10_CMD)". A
>few lines after that, after the "#endif" line, add the following
>(everything between but not including the ==== lines):
>
>=============================================================================
>/*
> * swab() was new in OSR506. Provide a version of it here, if needed.
> */
>#if !defined(WCE_BIT) /* WCE_BIT first appears in <sys/scsi.h> in OSR506 */
>void
>swab(src, dst, n)
>char *src;
>char *dst;
>int n;
>{
> while (n > 1) {
> n -= 2;
> dst[0] = src[1];
> dst[1] = src[0];
> src += 2;
> dst += 2;
> }
>}
>#endif
>=============================================================================
>
>Again, I think this will work but I haven't tested it. If you test it,
>please let me know (1) if you got it to link in, (2) if it booted, (3)
>if you saw any performance change.
>
>With the new driver, you can add a bootstring "wd.debug=iug". The
>letters are 'i' for IDE controller identification, 'u' for UDMA
>configuration and 'g' for geometry determination. It might be
>interesting to boot with "wd.debug=u" once with each hard drive, see if
>the configurations differ.
>
>>Bela<

Read your advice for this soul and used also.
I've noticed the same problems with a few of our machines
and your wisdom above did the trick!

Thanks,
jerry

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