03-03-2005
iostat -e / -E output explanation
Hi all, hope you are having a nice day, its nice and warm today in Canberra Australia.
iostat -e / -E reports soft and hard errors. Any idea what these are exactly? All I hear are I/O's failing and needing to retry, but no cause as to why they fail.
My SUN guru tells me its our EMC SAN array generating RSCN's or other fibre channle stuff, and the qlogic card then logs back into the fabric, and during that process some I/O has failed. However the iostat errors come up regardless of the EMC san.
I have searched for and read articles, etc, and really found nothing. however one article said the scsi driver doesn't know the disk RPM speed, another saying that SUN array software needs to be turned off.
We have a history with SUNmc causing SAN disk problems by constantly polling the disk for information (which is why we are upgrading it and have turned it off on some servers).
If you have lots of soft errors, are you likely to get a hard error? When you have lots of hard errors (eg, an internal disk is reporting 2400 hard errors with no corresponsing /var/adm/message entries to do with RSCN, scsi, etc) will you end up with track/cylinder errors?
I guess database/application issues will also cause I/O retries just like tcpip.
The number of network output/inpuit/collisions/queues, also do not relate to the iostat -e output.
Many Thanks
take care all
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IOSTAT(1) General Commands Manual IOSTAT(1)
NAME
iostat - report I/O statistics
SYNOPSIS
iostat [ drives ] [ interval [ count ] ]
DESCRIPTION
Iostat iteratively reports the number of characters read and written to terminals per second, and, for each disk, the number of transfers
per second, kilobytes transferred per second, and the milliseconds per average seek. It also gives the percentage of time the system has
spent in user mode, in user mode running low priority (niced) processes, in system mode, and idling.
To compute this information, for each disk, seeks and data transfer completions and number of words transferred are counted; for terminals
collectively, the number of input and output characters are counted. Also, each sixtieth of a second, the state of each disk is examined
and a tally is made if the disk is active. From these numbers and given the transfer rates of the devices it is possible to determine
average seek times for each device.
The optional interval argument causes iostat to report once each interval seconds. The first report is for all time since a reboot and
each subsequent report is for the last interval only.
The optional count argument restricts the number of reports.
If more than 4 disk drives are configured in the system, iostat displays only the first 4 drives, with priority given to Massbus disk
drives (i.e. if both Unibus and Massbus drives are present and the total number of drives exceeds 4, then some number of Unibus drives will
not be displayed in favor of the Massbus drives). To force iostat to display specific drives, their names may be supplied on the command
line.
FILES
/dev/kmem
/vmunix
SEE ALSO
vmstat(1)
4th Berkeley Distribution April 29, 1985 IOSTAT(1)