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Full Discussion: What process is writing to disk?
Top Forums UNIX for Advanced & Expert Users What process is writing to disk? Post 302252683 by radoulov on Thursday 30th of October 2008 05:43:20 AM
Old 10-30-2008
I would definitely try to trace the rest of the processes one by one (not exactly, here I'm tracing the mysqld process and follow the forks).
Something like this:

Code:
strace -Tfe pwrite64 -p <pid>

Code:
# strace -Tfe pwrite64 -p 2158
Process 32381 attached with 19 threads - interrupt to quit
[pid 32381] pwrite64(10, "\200>u\327\0\364\0\21\0\0\336\0178^\202\\\37&\0\201\307\0\2\0\2\200\4\200\0048\333\2"..., 512, 4721664) = 512 <0.000042>
[pid 32381] pwrite64(10, "\200>u\327\1\324\0\21\0\0\336\0178^\202\\\37&\0\201\307\0\2\0\2\200\4\200\0048\333\2"..., 512, 4721664) = 512 <0.000021>
[pid 32381] pwrite64(10, "\200>u\327\2\0\0\21\0\0\336\0178^\202\\\37&\0\201\307\0\2\0\2\200\4\200\0048\333\2"..., 1024, 4721664) = 1024 <0.000022>
[pid  2170] pwrite64(4, "\22\177\266\324\0\0\0007\377\377\377\377\377\377\377\377\0\0\0\0|\353\254\364\0\2\0\0\0\0\0\0"..., 81920, 1048576) = 81920 <0.000117>
[pid  2164] pwrite64(4, "2`\32e\0\0\0\5\0\0\0\0\0\0\0\0\0\0\0\0|\353\256\303\0\0\0\0\0\0\0\0"..., 32768, 81920) = 32768 <0.000095>
[pid  2164] pwrite64(4, "\22\177\266\324\0\0\0007\377\377\377\377\377\377\377\377\0\0\0\0|\353\254\364\0\2\0\0\0\0\0\0"..., 16384, 901120) = 16384 <0.000073>
[pid  2164] pwrite64(4, "Fd7\370\0\0\r{\377\377\377\377\377\377\377\377\0\0\0\0|\353\256YE\277\0\0\0\0\0\0"..., 16384, 56541184) = 16384 <0.000067>
[pid  2164] pwrite64(4, "\247\30\243\257\0\0\25\340\0\0\24\34\0\0\24:\0\0\0\0|\353\256\303\0\2\0\0\0\0\0\0"..., 16384, 91750400) = 16384 <0.000067>
[pid  2162] pwrite64(9, "\0\0\0\0\0\0\336\17\0\0\0\0|\353\256\303\0\230\16\303\0\20\0\0\377\377\377\377\377\377\377\377"..., 512, 1536) = 512 <0.000070>

Or use -c to count write system calls.

This should show the write intensive processes.
 

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LEARN ABOUT PLAN9

wren

WREN(3) 						     Library Functions Manual							   WREN(3)

NAME

       wren, ata - hard disk interface

SYNOPSIS

       bind #H[drive] /dev
       bind #w[target[.lun]] /dev

       /dev/hd0disk
       /dev/hd0partition
       /dev/sd0disk
       /dev/sd0partition
	...

DESCRIPTION

       The  hard  disk interfaces (wren, #w, is a SCSI disk; ata, #H, is an IDE or ATA disk) serve a one-level directory giving access to the hard
       disk partitions.  The parameter to attach defines the numerical SCSI target and logical unit number or the  IDE	drive  number  to  access.
       Both default to zero.

       Each  partition name is prefixed by hd and the numeric drive identifier.  The partition always exists and covers the entire disk.  The size
       of each partition as reported by stat(2) is the number of bytes in the partition, so the size of is the size of the entire disk.

       The partition also always exists; it is the last block on the disk for SCSI, second to last for IDE.  If it contains valid partition  data,
       those  partitions will be visible as well.  Every time the device is bound, the partitions are updated to reflect any changes in the parti-
       tion file.

       The format of the partition file is the string

	      plan9 partitions

       on a line, followed by partition specifications, one per line, consisting of a name and textual strings for the block start and	limit  for
       each partition on the disk.

       The program prep(8) writes the partition table for the disk; its use is preferred to writing it by hand.

SEE ALSO

       prep(8), scsi(3)

SOURCE

       /sys/src/9/port/devwren.c
       /sys/src/9/pc/devata.c

																	   WREN(3)
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