SAN Technology
iSCSI
- iSCSI Basics <== recommended
- Comments on block level storage and what it means
- Intro to iSCSI
- iSCSI on Linux
- iSCSI Initiator and Target Configuration
- Install and Manage iSCSI Volume (Linux/CentOS /Fedora Linux)
- Setting up LUNs on Linux
- Multiple Hosts for a single iSCSI Target
- Enhancing iSCSI Performance
- Another detailed example of iSCSI setup: mirrored volumes for redundancy
iSCSI emulates a SCSI interface over the network. The client ("initiator" in iSCSI terminology) accesses remote storage as a block device, e.g. an attached disk.
Having multiple initiators accessing same "target" (assuming it's configured with a single partition) is not trivial. This technology is essentially emulation of SCSI and not intended for sharing. It can be done with lots of effort and caveats.
Clients accessing different partitions can be expected to operate normally but of course there is no shared data in this case and there can be network congestion issues.
MC/S means multiple connections per session and it improves scalability and performance of a iSCSI installation. This feature is not supported in the standard part of Linux kernel (the initiator) called Open-iSCSI. There is a commercial software ("core-iSCSI") that does that.
It is important to remember that iSCSI works at the kernel level, whereas storage federation like XRootD is the user space.
Much of the same logic applies to the Fibre Channel technology. It is required that the SAN is equipped with cluster-aware filesystem for sharing to work.
iSCSI targets can have multiple NICs. Configuring those will require some work.
Redundancy can be achieved using LVM mirroring. This is in addition to a different possibility, which is to RAID disks in the iSCSI target which is a common practice in enterprise environments.
Fibre Channel
Fibre Channel Protocol is a network protocol (just like TCP is one). It is often used to transmit SCSI commands via a network in which case it's conceptually very similar to iSCSI. There are a few generations of the FC technology. It can utilize an optical connection (which was the original version that gave this technology its name) and also copper connections.
