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<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff size=2>>
Is there a critical reason to leave the SCSI timeout at 30 seconds
?</FONT></SPAN></DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff
size=2>Yes, On busy arrays (lots of queued command), even 30 seconds is
not sufficient. Our testing on heavily loaded arrays</FONT></SPAN></DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff size=2>says
i/o timeouts should actually be in the 60 second range. These
measurements were on standard single-path</FONT></SPAN></DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff
size=2>configs. You could argue that multipath configs make the queuing
worse. Also, background array tasks, such as</FONT></SPAN></DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff size=2>driver
rebuilds, etc </FONT></SPAN><SPAN class=099082714-13092005><FONT face=Arial
color=#0000ff size=2>will increase the normal i/o execution
times.</FONT></SPAN></DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff size=2>This
said, smart administrators should be monitoring i/o load, adjusting queue
depths, etc so that things aren't in the</FONT></SPAN></DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff size=2>range
of 30 seconds. However, with multipathing in the mix, this becomes a much more
difficult task for the admin.</FONT></SPAN></DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff size=2>Please
note: it is bad to assume what the command execution time latency is based
simply on having physical</FONT></SPAN></DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff
size=2>connectivity.</FONT></SPAN></DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff size=2>My
personal opinion is that you really want a "cancel i/o" interface. This way, at
least when you get notified of</FONT></SPAN></DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff size=2>the
loss of connectivity, you can cancel the remaining i/o's and failover quicker. I
would assume, in much the same way</FONT></SPAN></DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff size=2>as the
generic status codes are being handled, the block layer can be expanded to add
this interface (and call the</FONT></SPAN></DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff size=2>SCSI
abort handler, which already exists).</FONT></SPAN></DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=099082714-13092005><FONT face=Arial color=#0000ff size=2>--
james</FONT></SPAN></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px solid; MARGIN-RIGHT: 0px">
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> dm-devel-bounces@redhat.com
[mailto:dm-devel-bounces@redhat.com]<B>On Behalf Of
</B>gauri@etri.re.kr<BR><B>Sent:</B> Monday, September 12, 2005 10:52
PM<BR><B>To:</B> dm-devel@redhat.com<BR><B>Subject:</B> [dm-devel] How about
shortening SCSI timeout value dynamically?<BR><BR></FONT></DIV>
<DIV class=Section1 style="LAYOUT-GRID: 18pt none">
<P class=MsoNormal><FONT face=±¼¸² size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">Under
the <SPAN class=SpellE>multipath</SPAN> environment, when the path is
determined to fail, we have to wait 30 seconds because of the SCSI command
default <SPAN class=GramE>timeout(</SPAN>30 seconds). If the multiple paths
are alive, I think it is more efficient to short the SCSI command timeout.
Then we can shorten the delay of failover.<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=±¼¸² size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">Is
there any critical reason to remain SCSI timeout <SPAN class=GramE>as a</SPAN>
30 seconds?<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=±¼¸² size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=±¼¸² size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">What
do you think about my
this?<o:p></o:p></SPAN></FONT></P></DIV></BLOCKQUOTE></BODY></HTML>