Poor Disk Performance

Brendan Gregg

People often tell me they don't understand performance tool output because they can't tell what's "good" or "bad." It can be hard as performance is subjective. What's good for one user may be bad for another.

Poor Disk Performance

Brendan Gregg

Here's the biolatency(1) histograms when the disk is running faster: disk = 'sdb' usecs : count distribution 0 -> 1 : 0 | | 2 -> 3 : 0 | | 4 -> 7 : 0 | | 8 -> 15 : 0 | | 16 -> 31 : 0 | | 32 -> 63 : 0 | | 64 -> 127 : 0 | | 128 -> 255 : 0 | | 256 -> 511 : 0 | | 512 -> 1023 : 0 | | 1024 -> 2047 : 13 | | 2048 -> 4095 : 82 | *| 4096 -> 8191 : 0 | | 8192 -> 16383 : 9 | * | 16384 -> 32767 : 7 | | 32768 -> 65535 : 41 | ** | 65536 -> 131071 : 77 | * | 131072 -> 262143 : 2 | | 262144 -> 524287 : 1 | |.