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<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=807473315-29092006><FONT face=Arial color=#0000ff size=2>I suggest you use
the dm-multipath mapped device names instead of the target device ones.
Otherwise, you can run into problems caused by the fact that the cached
partition table for each of the possibly multiple target paths are not kept
in synch with the partition table of the multipath mapped
device.</FONT></SPAN></FONT></DIV>
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class=807473315-29092006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=807473315-29092006><FONT face=Arial color=#0000ff size=2>In this case,
fdisk is failing because it attempts to read the partition table (MBR block 0)
of the disk and /dev/sdq is the passive path to the disk. This is correct
behavior for Linux dm-multipath since it does not attempt to provide
multipathing for accesses to the target device paths, e.g.,
/dev/sdq.</FONT></SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=807473315-29092006></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=807473315-29092006></SPAN><SPAN class=807473315-29092006><FONT face=Arial
color=#0000ff size=2>Also, be careful because this behavior can be intermittent
since this operation would have succeeded if this logical block was resident in
the page cache, which could happen if /dev/sdq was an active path to the logical
unit just a little while beforehand.</FONT></SPAN></FONT><BR></DIV>
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<FONT face=Tahoma size=2><B>From:</B> dm-devel-bounces@redhat.com
[mailto:dm-devel-bounces@redhat.com] <B>On Behalf Of </B>Herr,
Manuel<BR><B>Sent:</B> Thursday, September 28, 2006 6:03 AM<BR><B>To:</B>
dm-devel@redhat.com<BR><B>Subject:</B> [dm-devel] Device Access
Question<BR></FONT><BR></DIV>
<DIV></DIV><!-- Converted from text/rtf format -->
<P><FONT face=Arial size=2>Is it correct that if an LUN is seen over 2
Paths,</FONT> <BR><FONT face=Arial size=2>1 active 1 standby i cannot fdisk
the standby device?</FONT> <BR></P>
<P><FONT face=Arial size=2>#multipath -l</FONT> <BR><FONT face=Arial
size=2>(3600601604032190097fd5fbefd22db11)</FONT> <BR><FONT face=Arial
size=2>[size=11 GB][features="1 queue_if_no_path"][hwhandler="1 emc"]</FONT>
<BR><FONT face=Arial size=2>\_ round-robin 0 [active]</FONT> <BR><FONT
face=Arial size=2> \_ 3:0:0:7 sdi 8:128 [active][ready]</FONT> <BR><FONT
face=Arial size=2>\_ round-robin 0 [enabled]</FONT> <BR><FONT face=Arial
size=2> \_ 3:0:1:7 sdq 65:0 [active][ready]</FONT> </P>
<P><FONT face=Arial size=2>#fdisk -l /dev/sdi</FONT> <BR><FONT face=Arial
size=2>Disk /dev/sdi: 11.8 GB, 11811160064 bytes</FONT> <BR><FONT face=Arial
size=2>255 heads, 63 sectors/track, 1435 cylinders</FONT> <BR><FONT face=Arial
size=2>Units = cylinders of 16065 * 512 = 8225280 bytes</FONT> </P>
<P><FONT face=Arial size=2> Device
Boot
Start
End Blocks Id System</FONT>
<BR><FONT face=Arial
size=2>/dev/sdi1
1 1435
11526606 83 Linux</FONT> </P>
<P><FONT face=Arial size=2>#fdisk -l /dev/sdq</FONT> <BR><FONT face=Arial
size=2>--> creates in /var/log/messages</FONT> <BR><FONT face=Arial
size=2>Sep 28 12:01:22 saptf2 kernel: end_request: I/O error, dev sdq, sector
0</FONT> <BR><FONT face=Arial size=2>Sep 28 12:01:22 saptf2 kernel: Buffer I/O
error on device sdq, logical block 0</FONT> </P>
<P><FONT face=Arial size=2>Regards Manuel Herr</FONT>
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