Slow on heavy I/O operations.

[Oliver Fromme]

Roman Gorohov. <roma.a.g at gmail.com> wrote:
 > Hello list.
 > There is a server with FreeBSD FreeBSD 4.11-STABLE(can't upgrade fornow) on HP ProLiant DL140.
 > Disk system: <SEAGATE ST373207LC 0005> at scbus0 target 0 lun0(pass0,da0) on a ASC-29320A.
 > If I do:
 > [idle at hst ~]#dd if=/dev/zero of=bigfile bs=64k count=5000
 > 5000+0 records in
 > 5000+0 records out
 > 327680000 bytes transferred in 37.515699 secs (8734477 bytes/sec)
 > All is hung while dd working.
 > 
 > Its look like that:
 > [idle at hst ~]#systat -v
 > skip...
 > Disks   da0 pass0 pass1   md0         
 > KB/t  20.33  0.00  0.00  0.00        
 > tps     812     0     0     0        
 > MB/s  16.11  0.00  0.00  0.00                      
 > % busy  100     0     0     0                                                               
 > skip...
 > 
 > [idle at hst ~]#vmstat -w 5
 >  procs      memory      page                    disks     faults      cpu
 >  r b w     avm    fre  flt  re  pi  po  fr  sr da0 md0   in   sy  cs us sy id
 >  1 0 0 1996756  54208   42  23  25   7  39 336   0   0  531  638 404 21  5 74
 >  1 6 0 2011488  13272  571   0   0   1 2506   8 129   0 1356 2125 159  3  4 93
 >  4 27 0 2022852   4228  267   0   0   1 1657   4 272   0 1450  784  96  1  3 96
 >  1 10 0 2027492  40220  449   5   0  12 3257 9384 574   0 1773 4366 189  8  7 85
 >  1 10 0 2035064  25604  746   2   1   7 2965 4466 157   0 1380 4486 184  8  7 85
 >  0 11 0 2030860   4228  515   2   1   3 2098  31 214   0 1412 3077 149 16  5 79
 >  3 14 0 2042792  10004 1014   4   1   5 2787 4432 267   0 1440 1735 118  2  4 94
 >  2 16 0 2062664   4228  301   0   1   2 2843  27 564   0 1759 1250 107  5  4 91
 > 
 > [idle at hst ~]#iostat -w 5
 >       tty             da0            pass0            pass1             cpu
 >  tin tout  KB/t tps  MB/s   KB/t tps  MB/s   KB/t tps  MB/s  us ni sy in id
 >    0   25  0.00   0  0.00   0.00   0  0.00   0.00   0  0.00  21  0  4  0 74
 >    1  109 62.56 242 14.81   0.00   0  0.00   0.00   0  0.00   7  0  9  0 83
 >    0  101 18.29 433  7.73   0.00   0  0.00   0.00   0  0.00   2  0  2  0 95
 >    0   76 26.45 281  7.25   0.00   0  0.00   0.00   0  0.00   3  0  4  0 93
 >    0   94 15.99 357  5.57   0.00   0  0.00   0.00   0  0.00   2  0  2  0 96
 >    0   15 16.04 667 10.45   0.00   0  0.00   0.00   0  0.00   0  0  3  1 96
 >    0   93 15.99 558  8.71   0.00   0  0.00   0.00   0  0.00   0  0  2  1 97
 >    0   80 16.16 252  3.98   0.00   0  0.00   0.00   0  0.00   0  0  1  0 98
 >    0  117 23.44 240  5.49   0.00   0  0.00   0.00   0  0.00   9  0  6  0 85
 > 
 > Why this happen?

The numbers from your vmstat output indicate that your
machine is paging ("swapping"), i.e. it's running out
or RAM.

Of course, such paging activity competes with other I/O
operations in the system, which explains the symptoms
that you're seeing.

 > What should I do?

Either add more RAM, or reduce the memory requirements
of your applications, if possible.

Another work-around wold be to add a second disk and use
it exclusively for swap.  That way it won't compete with
I/O operations on yoru data disk.  The paging will still
slow down your machine, though, therefore you should
really try to add more RAM.

Best regards
   Oliver

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