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<DIV>Hi,all</DIV>
<DIV> </DIV>
<DIV>In my experiment I found a very strange thing: No write hit in on-board disk cache!</DIV>
<DIV>I use the validate trace as following:</DIV>
<DIV><FONT color=#0000ff></FONT> </DIV>
<DIV><FONT
color=#0000ff>W Hit 5568004 8 1464.00000 53368.00000
</FONT><FONT color=#000000>---request 1--</FONT></DIV>
<DIV><FONT
color=#0000ff>W Hit 5568012 8 1323.00000 54353.00000 </FONT><FONT
color=#000000>---request 2--</FONT></DIV>
<DIV><FONT
color=#0000ff>W Hit 1505868 4 1098.00000 32082.00000
</FONT><FONT color=#000000>---request 3--</FONT></DIV>
<DIV><FONT
color=#0000ff>W Hit 1505868 4 879.00000 39461.00000
</FONT><FONT color=#000000>---request 4--</FONT></DIV>
<DIV> </DIV>
<DIV># ./disksim cheetah9LP.parv file_1 validate trace 0</DIV>
<DIV> </DIV>
<DIV>But no hit found in the file_1. Theoretically there should be a write
combine with request 1 and 2. Also a write hit with 4 after 3. But indeed there
is no.</DIV>
<DIV> </DIV>
<DIV>I tracked the <FONT
color=#ff00ff>disk_buffer_select_write_segment</FONT> and <FONT
color=#ff00ff>disk_release_hda</FONT> function. There is no conserve of write
although I use the fast write mode. A new request own a segment for
write and release it after completion.</DIV>
<DIV> </DIV>
<DIV>And I increased the segment counts in the cheetah9LP.diskspecs. There is
litter increase(less than 1%) about the cache hit ratio! (with command
./disksim cheetah9LP.parv file_1 validate cheetah9LP.trace 0)</DIV>
<DIV> </DIV>
<DIV>Does this really the cache management for modern disk? </DIV>
<DIV> </DIV>
<DIV>I think the fast write mode enabled can conserve more small write and then
write them optimizely (sometime sequentially write or with freeblock scheduling
policy).</DIV>
<DIV>
<DIV> </DIV>
<DIV>Thank you for your discussion.</DIV></DIV>
<DIV>------------------ </DIV>
<DIV>mb</DIV>
<DIV>2007-09-02</DIV>
<DIV> </DIV>
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