Maurilio,
after successfully testing iscsi boot of a xp client pc using
iscsitgtd I decided to try to use COMSTAR as iscsi target software
since everybody seems to agree that it is the future and has far
better speed.
Now, after spending this afternoon checking and redoing the basic
steps to export a zvol as a lun through comstar just to see the xp
client (booting through gPXE) fail to boot I started looking around
for some clue till I found out this bug id: 6701531
It says that sbd (which I think is the sbdadm program) writes LU
metadata on the first 64KB of the backing store (my zvol in this
case).
So, I do a dd of the xp hard disk to a zvol but as soon as I issue
the sbdadm create-lu command it destroys the first 64KB of that disk
image making boot impossibile (in fact, gPXE stops saying it can not
boot from the disk).
Now, please, tell me this is not true .) How can copy a disk image
to a zvol preserving the image integrity? How can I create a LU from
a zvol which already has data inside (think about moving iscsitgtd
exported zvols to comstar)?
Use the iscsi initiator software 'man iscsiadm', to access the COMSTAR
iSCSI Target LUN using the loopback address of 127.0.0.1. Then
partition (on i386 systems), and then format the SCSI LUN. This is
required since the first time the new iSCSI LUN is accessed, it will
be an unformatted disk, likely containing random data.
Recall that for a SCSI device to be accessible to Solaris on an i386
platform, it must first be partitioned with 'fdisk', a command-line
utility that provides disk partitioning functions to an operating
system. Then for both i386 and SPARC platforms, the disk then needs
either a VTOC or EFI disk label. Once partitioned and label, the disk
is now accessible by Solaris.
Note the partitioning a disk (i386), and placing an volume label on an
iSCSI LUN, consumes addition disk blocks. Therefore copying data to
the backing store device given to COMSTAR (or even the old iSCSI
Target Daemon) is just not practical.
A quick means to partition and format a new SCSI LUN, which also
places all available blocks in partition 0, is to issue the following
two commands:
zpool create temp <SCSI device name>
zpool destroy temp
NOTE: If this disk space was once a ZFS vdev, the optional -f (force)
option may need to specified on the first command.
- Jim
Maurilio.
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