06-29-2004
First think about disk arrays. A disk array might plug into a computer's scsi interface. The computer doesn't see the real disks. It sees make-believe disks provided by the array. You typically connect to a serial port on the disk array to program exactly what these disks look like. But to the computer, the disk seem like local disks. It can build a filesystem and mount it. Or it can use the raw disk space as with a database. You would usually mount the disk, but this is not absolutely required.
Next, instead of that scsi inteface, imagine a computer that talks to an attached disk array via fibre channel. We actually have several of these. You need fibre channel drivers on the computer. But no other special software.
Now unplug that fibre channel cable from the disk array and plug it into a SAN server. A SAN server is just a disk array on steroids....lots of steriods. Dozens of computers connect to it. You telnet into the SAN server to define what the make-believe disks look like but once again, to the computer they are just local disks.
SANs do have additional features beyond what a disk array can do to support clustering and backups, but to just get a handle on it, just think of it as a massive super disk array.
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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)