Some notes on Solaris 10 U4 x86 as an iSCSI target

November 5, 2007

The latest release of Solaris 10 (S10U4 or 8/07 depending on how you like to label it) has a built in iSCSI target implementation, and ZFS even has integration with it so that it is easy to export space from ZFS pools. I've been poking it a bit, resulting in some things I want to note down for my own later reference.

  • Solaris 10 iSCSI target stuff is handled with the iscsitadm command, which is helpfully only one letter away from the iscsiadm command to administer Solaris iSCSI initiator settings. The two commands are very similar and take options in the same way, except when they pick different vocabulary for the same command; iscsiadm uses 'add' and 'remove', but iscsitadm uses 'create' and 'delete'.

    (It is possible that this difference is deliberate, in order to prevent accidentally doing an operation with the wrong program. The fly in the ointment is that the command options are generally completely different, so I'm pretty sure that the attempted operation would fail anyways.)

  • the very first thing you need to do is use iscsitadm modify admin -d <dir> to tell the iSCSI target stuff where to store state information, like what targets you've defined. If you do not do this, nothing will complain, but (among other things) all of the targets you've carefully manually defined will disappear when you reboot.

    (I think ZFS targets created with the shareiscsi ZFS property might still persist.)

  • in targets with multiple LUNs, you should make LUN 0 (the first one created) be a little dummy LUN that never actually gets used (a few megabytes of backing file will do). This is because you cannot modify LUNs except by deleting and recreating them, and you cannot delete LUN 0 unless there's no other LUN.

  • setting the ZFS shareiscsi property creates a separate iSCSI target for every shared ZVOL, even if they're inheriting the property from a filesystem. If you need to bundle things into multiple LUNs on the same target, you will need to do things by hand.

  • there seems to be no way to manually set the iSCSI name of a target when you create it. This seems unfortunate and limiting, since there are a number of situations where you need to set the iSCSI name to something specific.

  • iscsitgtd periodically dumps core in /, sometimes with multi-gigabyte core files that will fill up your root filesystem (I have seen it dump over a 5 gigabyte core file).

In general iscsitadm seems biased towards creating a new iSCSI target for every separate bit of target storage that you have. If you are using one of the dynamic discovery methods on your iSCSI initiators this is not too bad, but it is going to be horrible if you're using a static configuration; for static configurations you really want LUNs within a single iSCSI target.

Written on 05 November 2007.
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Last modified: Mon Nov 5 23:31:15 2007
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