Related articles * [iSCSI Target](/index.php/ISCSI_Target "ISCSI Target") * [iSCSI Boot](/index.php/ISCSI_Boot "ISCSI Boot") The [TGT SCSI framework](http://stgt.sourceforge.net) can be used for several storage protocols. This document describes the usage of TGT as iSCSI target. ## Contents * [1 About TGT](#About_TGT) * [2 Installation](#Installation) * [3 Configuration](#Configuration) * [4 Example configuration](#Example_configuration) * [5 Start](#Start) * [6 See also](#See_also) ## About TGT 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. Advantages: * active development * simplicity * 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. ## Installation Install the [tgt](https://aur.archlinux.org/packages/tgt/) package or [tgt-rdma](https://aur.archlinux.org/packages/tgt-rdma/) package, if you plan on using iSER. If you want to use the direct store, then [sg3_utils](https://www.archlinux.org/packages/?name=sg3_utils) 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](/index.php/Firewall "Firewall"), tcp port 3260 should be open. ## Configuration The configuration can be done: * using the `tgtadm` utility, afterwards you can use `tgt-admin --dump` to save the configuration. `tgt-admin` is a Perl script that parses `/etc/tgt/targets.conf` and configures tgt. You can find this method in the [Scsi-target-utils Quickstart Guide](http://fedoraproject.org/wiki/Scsi-target-utils_Quickstart_Guide), as linked from the [TGT website](http://stgt.sourceforge.net). * editing the /etc/tgt/targets.conf file. STGT supports multiple configurations. Include other config files in the main configuration file: `include /etc/tgt/*.conf` * manual configuration: Create a target: ``` tgtadm --lld iscsi --op new --mode target --tid -T ``` Allow only connection from specific initiators: ``` tgtadm --lld iscsi --op bind --mode target --tid --initiator-name ``` or using the initiator IP: ``` tgtadm --lld iscsi --op bind --mode target --tid --initiator-address ``` Map a LUN to the target: ``` tgtadm --lld iscsi --op new --mode logicalunit --tid --lun -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 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 ``` Save configuration: ``` tgt-admin --dump > /etc/tgt/targets.conf ``` Reload configuration: ``` tgt-admin --update ALL ``` This command only updates targets that are not in use. Use '--force' to update targets that are in use. ## Example configuration ``` direct-store /dev/sdb write-cache on initiator-address ALL incominguser user password scsi_id 00010001 vendor_id XTG lun 12 ``` ``` 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](http://www.ietf.org/rfc/rfc3720.txt) ## Start STGT can be [started/enabled](/index.php/Started/enabled "Started/enabled") with the `tgtd.service` unit. You can check if everything works as expected: ``` tgt-admin -s ``` ## See also * [Quickstart Guide for STGT for Fedora](https://fedoraproject.org/wiki/Scsi-target-utils_Quickstart_Guide) * [Configuration File Guide](http://wpkg.org/TGT-admin)