TGT iSCSI Target
The TGT SCSI framework can be used for several storage protocols. This document describes the usage of TGT as iSCSI target.
STGT was introduced into the Linux kernel at the end of 2006 by Fujita Tomonori. It has a library in the kernel which assists the in-kernel target drivers. All target processing happens in user space. At the end of 2010, the LIO project was chosen to replace STGT as the in-kernel SCSI target implementation. When LIO was chosen to replace STGT, its implementation has been adapted to allow STGT userspace modules to continue functioning, therefore the STGT community has supported the LIO inclusion in the kernel.
- active development
- support for iSCSI for Ethernet NICs, iSER, virtual SCSI target driver for IBM pSeries
- supports virtual disks, DVDs, VTLs, RADOS block devices (rbd)
- supports SCSI UNMAP
As a disadvantage some developers and users have argued that because the target processing happens in user space, in some cases this may lead to performance bottlenecks. However, using 'aio' type LUNs gives a huge performance boost. AIO should only be used in environments that are safe against power loss.
Install theAUR package or AUR package, if you plan on using iSER. If you want to use the direct store, then must also be installed.
Using direct-store, the properties of the physical device will be available for the initiator and target.
Please notice, if you're using a Firewall, tcp port 3260 should be open.
The configuration can be done:
- using the
tgtadmutility, afterwards you can use
tgt-admin --dumpto save the configuration.
tgt-adminis a Perl script that parses
/etc/tgt/targets.confand configures tgt. You can find this method in the Scsi-target-utils Quickstart Guide, as linked from the TGT website.
- editing the /etc/tgt/targets.conf file. STGT supports multiple configurations. Include other config files in the main configuration file:
- manual configuration:
Create a target:
tgtadm --lld iscsi --op new --mode target --tid <unique target ID> -T <unique iSCSI iqn>
Allow only connection from specific initiators:
tgtadm --lld iscsi --op bind --mode target --tid <target ID> --initiator-name <initiator IQN>
or using the initiator IP:
tgtadm --lld iscsi --op bind --mode target --tid <target ID> --initiator-address <initiator IP>
Map a LUN to the target:
tgtadm --lld iscsi --op new --mode logicalunit --tid <target ID> --lun <unique LUN ID> -b /path_to/lun.img
LUN ID must be a non-zero decimal value. LUN 0 is reserved for the target controller.
For ESXi it is very important to map LUNs with persistent LUN IDs. If the LUN on the storage system changes its ID, ESXi will not be able to automatically remount it, and will trigger a PDL condition. Use direct-store instead of backing-store to define LUN IDs which will be persistent across reboots.
View current configuration:
tgtadm --op show --mode target --tid <target ID> MaxRecvDataSegmentLength=8192 HeaderDigest=None DataDigest=None InitialR2T=Yes MaxOutstandingR2T=1 ImmediateData=Yes FirstBurstLength=65536 MaxBurstLength=262144 DataPDUInOrder=Yes DataSequenceInOrder=Yes ErrorRecoveryLevel=0 IFMarker=No OFMarker=No DefaultTime2Wait=2 DefaultTime2Retain=20 OFMarkInt=Reject IFMarkInt=Reject MaxConnections=1 RDMAExtensions=Yes TargetRecvDataSegmentLength=262144 InitiatorRecvDataSegmentLength=262144 MaxOutstandingUnexpectedPDUs=0 MaxXmitDataSegmentLength=8192 MaxQueueCmd=128
tgt-admin --dump > /etc/tgt/targets.conf
tgt-admin --update ALL
This command only updates targets that are not in use. Use '--force' to update targets that are in use.
<target iqn.2004-01.nl.xtg:iscsi-server1> direct-store /dev/sdb write-cache on initiator-address ALL incominguser user password scsi_id 00010001 vendor_id XTG lun 12 </target>
MaxRecvDataSegmentLength 131072 MaxXmitDataSegmentLength 131072 MaxBurstLength 262144 FirstBurstLength 262144 TargetRecvDataSegmentLength=262144 InitiatorRecvDataSegmentLength=262144 MaxOutstandingUnexpectedPDUs=0 MaxOutstandingR2T=1 MaxCommands=128
In the first part of this example, /dev/sdb will be mapped as LUN 12 and chap authentication is configured. In the second part are some iSCSI advanced parameters
STGT can be started/enabled with the
You can check if everything works as expected: