Bug 121716 - (IT_52396) Raw device I/O transfer size limited to 32KB.
Raw device I/O transfer size limited to 32KB.
Product: Red Hat Enterprise Linux 3
Classification: Red Hat
Component: kernel (Show other bugs)
i686 Linux
medium Severity medium
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Assigned To: Stephen Tweedie
Brian Brock
Depends On: 131391
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Reported: 2004-04-26 14:18 EDT by Keith Kauffman
Modified: 2007-11-30 17:07 EST (History)
7 users (show)

See Also:
Fixed In Version:
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Last Closed: 2005-05-18 09:27:22 EDT
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RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

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External Trackers
Tracker ID Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2005:294 normal SHIPPED_LIVE Moderate: Updated kernel packages available for Red Hat Enterprise Linux 3 Update 5 2005-05-18 00:00:00 EDT

  None (edit)
Description Keith Kauffman 2004-04-26 14:18:37 EDT
Description of problem:
After modifying the Qlogic HBA driver module to support large bock 
transfers, statistics were gathered that suggest to maximum transfer 
size was 32KB.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1. Modify the Qlogic HBA driver (versions 6.06.65, 6.06.00b11, 
6.06.10, and 7.00.00b23) to support large block transfers (qla2x00.h -
 SG_SEGMENTS defined as SG_ALL, max_sectors defined as 8192).
2. Compile and install driver.
   $make all install
3. Reload driver module
   $modprobe -r qla2300
   $modprobe -v qla2300
4. Use dd to issue reads to /dev/raw/raw1 (raw device bound 
to /dev/sdb - LSI RAID disk).
   $dd if=/dev/raw/raw1 of=/dev/null bs=512K count=1024
   $dd if=/dev/raw/raw1 of=/dev/null bs=512K count=1024
Actual results:
Maximum transfer size: 32KB

Expected results:
Maximum transfer size: 512KB

Additional info:
Comment 1 Keith Kauffman 2004-04-30 12:41:22 EDT
Kernel version 2.4.21-14 (from the beta channel) does not appear to 
resolve this issue with respect to raw devices.  The transfer size is 
still limited to 32K.  Block device transfer size was found to be 

Command executed:
dd if=/dev/raw/raw1 of=/dev/null bs=512k count=1000
(/dev/raw/raw1 bound to /dev/sda - LSI RAID disk)

(The assumption was made that 2.4.21-14 contains the same fixes as 
2.4.21-12 referenced in bug 104633.)

Red Hat 7.3 kernel version 2.4.20-28.7 does not exhibit this 
behavior.  The transfer size reported was 512K.
Comment 7 Stephen Tweedie 2005-03-03 09:57:32 EST
A patch to allow raw IOs ("superbh" IOs) larger than 32k has been committed for
the U5 kernel.
Comment 8 Ernie Petrides 2005-03-03 22:12:38 EST
The fix referred to in comment #7 was committed to the RHEL3 U5
patch pool on 23-Feb-2005 (in kernel version 2.4.21-28.EL).
Comment 9 Tim Powers 2005-05-18 09:27:22 EDT
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.


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