I have a process running in a CentOS 6.3 server. When logging is turned on, the process slows down drastically. The logs are being written to /tmp
[root@localhost src]# hdparm -I /dev/sda
/dev/sda:
SG_IO: bad/missing sense data, sb[]: 70 00 05 00 00 00 00 0d 00 00 00 00 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ATA device, with non-removable media
Standards:
Likely used: 1
Configuration:
Logical max current
cylinders 0 0
heads 0 0
sectors/track 0 0
--
Logical/Physical Sector size: 512 bytes
device size with M = 1024*1024: 0 MBytes
device size with M = 1000*1000: 0 MBytes
cache/buffer size = unknown
Capabilities:
IORDY not likely
Cannot perform double-word IO
R/W multiple sector transfer: not supported
DMA: not supported
PIO: pio0
[root@localhost src]# df -k
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/VolGroup-lv_root
51606140 6267948 42716752 13% /
tmpfs 8141564 1016 8140548 1% /dev/shm
/dev/sda3 495844 37728 432516 9% /boot
/dev/mapper/VolGroup-lv_home
1090839440 1022652 1034405284 1% /home
How do I figure out what is wrong here? And how to fix this? Thanks.
Edit:
lshw output:
[root@localhost src]# ./lshw -class disk
*-disk
description: SCSI Disk
product: PERC H310
vendor: DELL
physical id: 2.0.0
bus info: scsi@0:2.0.0
logical name: /dev/sda
version: 2.12
serial: 00677e1515fc98ef19000d93f7a0a38c
size: 1117GiB (1199GB)
capabilities: partitioned partitioned:dos
configuration: ansiversion=5 logicalsectorsize=512 sectorsize=512 signature=31c27a66
Best Answer
You haven't told us what the process is doing and if the process is writing to the same disk you are also logging to. If so, it shouldn't be a shock that writing to the same disk with the logging is going to slow the process that is also writing to disk. IF it is only a single spindle with what looks like an ATA disk spinning at likely 7.2k, you would be even more constrained by the number of IOPS that the single spindle can handle.
edit: The hdparm output also seems to indicate that your drive is running in PIO 0 mode and that DMA mode is not supported. DMA mode transfers should be faster, if it is really running in PIO mode 0, you are running the the slowest mode possible for the ATA interface.