iSCSI

iscsi allows one to share and mount block devices using the scsi protocol over a network. Fedora currently connects to a netapp that has an iscsi export.

Contents

Contact Information

Owner

Fedora Infrastructure Team

Contact

#fedora-admin, sysadmin-main

Servers

xen[1-15]

Purpose

Provides iscsi connectivity to our netapp.

Typical Uses

The best uses for Fedora are for servers that are not part of a farm or live replicated. For example, we wouldn’t put app1 on the iscsi share because we don’t gain anything from it. Shutting down app1 to move it isn’t an issue because app1 is part of our application server farm.

noc1, however, is not replicated. It’s a stand alone box that, at best, would have a non-live failover. By placing this host on an iscsi share, we can make it more highly available as it allows us to move that box around our virtualization infrastructure without rebooting it or even taking it down.

iscsi Basics

Terms

  • initiator means client

  • target means server

  • swab means mop

  • deck means floor

iscsi’s basic login / logout procedure is

  1. Notify your client that a new target is available (similar to editing /etc/fstab for a new nfs mount)

  2. Login to the iscsi target (similar to running "mount /my/nfs"

  3. Logout from the iscsi target (similar to running "umount /my/nfs"

  4. Delete the target from the client (similar to removing the nfs mount from /etc/fstab)

Logging in

Most mounts are covered by ansible so this should be automatic. In the event that something goes wrong though, the best way to fix this is:

  • Notify the client of the target:

    iscsiadm --mode node --targetname iqn.1992-08.com.netapp:sn.118047036 --portal 10.5.88.21:3260 -o new

  • Log in to the new target:

    iscsiadm --mode node --targetname iqn.1992-08.com.netapp:sn.118047036 --portal 10.5.88.21:3260 --login

  • Scan and activate lvm:

    pvscan
vgscan
vgchange -ay xenGuests

Once this is done, one should be able to run "lvs" to see the logical volumes

Logging out

Logging out isn’t normally needed, for example rebooting a machine automatically logs the initiator out. Should a problem arise though here are the steps:

  • Disable the logical volume:

    vgchange -an xenGuests

  • log out:

    iscsiadm --mode node --targetname iqn.1992-08.com.netapp:sn.118047036 --portal 10.5.88.21:3260 --logout

Cannot deactivate volume group

If the vgchange command fails with an error about not being able to deactivate the volume group, this means that one of the logical volumes is still in use. By running "lvs" you can get a list of volume groups. Look in the Attr column. There are 6 attrs listed. The 5th column usually has a - or an a. a means its active, - means it is not. To the right of that (the last column) you will see an - or an o. If you see an o that means that logical volume is still mounted and in use.

Note about creating new logical volumes

At present we do not have logical volume locking on the xen servers. This is dangerous and being worked on. Basically when you create a new volume on a host, you need to run:

pvscan
vgscan
lvscan

on the other virtualization servers.

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