11-13-2007
First off: if you tar something, the command will read something on your disk (a bunch of files) and then create an archive from it, writing that to the disk (most of times). What else then seeing activity on your disk do you suppose will happen?
Additionally i would like to clarify what the "% tm_act" field in the output of iostat means:
The OS has a sensor, regularily asking the disk if it is busy or not. When the disks aswers half of the times "I'm busy", then the "% tm_act" will be 50%. If the disk answers every time "I'm busy" then tm_act will be 100%, etc.. A disk answers with "busy", when there are requested operations not yet fulfilled, read or write. If many very small requests go to the disk the chance of the sensor asking exactly when one such operation is still open goes up - much more so than the real activity of the disk.
So, "100% busy" does not necessarily mean the disk is at the edge of its trasnfer bandwidth. It could mean either that because the disk is getting relatively few but big requests (example: stream I/O) but it could also mean that the disk is getting a lot of requests which are relatively small so that the disk is occupied most of the time, but not using its complete transfer bandwith.
To find out which is the case analyse the corresponding "Kb_read" and "Kb_wrtn" column from iostat. You know how much a modern disk drive can approximately handle (~17MB/second) physically and bypassing any cache. Compare your data to this (rule-of-thumb-)value and you will get a more detailed picture.
bakunin
Last edited by bakunin; 11-13-2007 at 08:42 AM..
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LEARN ABOUT HPUX
vxreattach
vxreattach(1M) vxreattach(1M)
NAME
vxreattach - reattach disk drives that have once again become accessible
SYNOPSIS
/etc/vx/bin/vxreattach [-br ] [accessname...]
/etc/vx/bin/vxreattach -c accessname
DESCRIPTION
The vxreattach utility reattaches disks to the disk group they were in and retains the same media name.
This operation may be necessary if a disk has a transient failure, or if Veritas Volume Manager (VxVM) starts with some disk drivers
unloaded and unloadable. Disks then enter the failed state. If the problem is fixed, vxreattach may be able to reattach the disks without
plexes being flagged as stale, as long as the reattach happens before any volumes on the disk are started.
vxreattach tries to find a disk in the same disk group with the same disk ID for the disk(s) to be reattached. The reattach operation may
fail even after finding the disk with the matching disk ID if the original cause (or some other cause) for the disk failure still exists.
vxreattach is usually invoked by vxdiskadm when performing disk recovery. It is not intended to be run directly by an administrator.
OPTIONS
-b Performs the reattach operation in the background.
-c Checks if a reattach is possible. No operation is performed, but the name of the disk group and disk media name at which the
disk can be reattached is displayed.
-r Tries to recover stale plexes of any volumes on the failed disk. It does this by calling vxrecover.
EXIT CODES
A zero exit status is returned if the reattach is performed; non-zero is returned otherwise.
See vxintro(1M) for a list of standard exit codes.
EXAMPLES
Check if reattachment of disk c1t2d0 is possible:
/etc/vx/bin/vxreattach -c c1t2d0
If reattachment is possible, vxreattach returns with an exit status of 0 and displays the disk group name and disk media name. If reat-
tachment is not possible, vxreattach returns an exit status of 2 and displays an error.
Attempt to reattach the disk in the foreground and try to recover stale plexes of any volumes on the disk:
/etc/vx/bin/vxreattach -r c1t2d0
If the reattachment is successful, vxreattach returns an exit status of 0. Otherwise, if an error occurs, vxreattach returns a non-zero
exit code as defined on vxintro(1M).
FILES
/etc/default/vxplex Standard defaults file that can be used to determine whether FastResync is used when attaching plexes. See vxplex(1M)
for details.
SEE ALSO
vxdiskadm(1M), vxintro(1M), vxplex(1M), vxrecover(1M)
VxVM 5.0.31.1 24 Mar 2008 vxreattach(1M)