Low Cost SAN - Page 3

8.2  Initiators (AoE)

This section describes about available AoE initiators. Client side AoE drivers are available on FOSS for Linux, Solaris, Free BSD as well as for windows. It is also available for Mac OS X, but it's paid. Following diagram shows it more clearly:

The brief description of available AoE initiators is as follows:

8.3  SAN diagram (based on AoE protocol)

This section describes the basic architecture of our SAN which is based on AoE protocol, AoE target (vblade) and AoE initiator (aoe driver).

In above diagram there are two servers: server0 and server1. Each of them exports two block devices on the network and client node access these block devices as a RAID device. Here from server0 /dev/hdb is exported as /dev/etherd/e0.0 & /dev/hdc is exported as /dev/etherd/e1.0. Similarly from server1, we have exported two block devices: /dev/hdb as /dev/etherd/e0.0 and /dev/hdc as /dev/etherd/e1.1. Now we have four block devices on client side. These are as follows:

•  /dev/etherd/e0.0 (from server0)

•  /dev/etherd/e0.1 (from server1)

•  /dev/etherd/e1.0 (from server0)

•  /dev/etherd/e1.1 (from server1)

Now we have combined /dev/etherd/e0.0 & /dev/etherd/e0.1 as a raid device (/dev/md0) having raid level 1 (mirroring) property. Similarly /dev/etherd/e1.0 and /dev/etherd/e1.1 is combined as a raid device (/dev/md1) having raid level 1(mirroring) property. Now we combined these two raid device as a single raid device (/dev/md2) which has raid level 0 (stripping property). So, finally we have a single raid device /dev/md2 (by the combination of four exported block device) on which we can easily make a file system and can use on client side for further work. We can also do volume management before creating the raid device.

8.4  HA/Failover

This section describes about SAN challenges and the available open source solutions against them. The quite obvious challenges of storage networking arena is as follows:

•  Storage

•  High Availability

•  Load Balancing

•  High Performance

•  Easily Manageable

To achieve these targets, we have a quite reliable tool which is known as RHCS (red hat clustering Suite). Redhat cluster suite can be used in many configurations in order to provide high availability, scalability, load balancing, file sharing, and high performance.

RHCS has following component to achieve above mentioned SAN challenges.

Apart from RHCS suite we have DRBD and HEARTBEAT also available against the HA solution on SAN or in any cluster. They are on FOSS. The brief descriptions of these softwares are as follows:

•  DRBD: DRBD ( Distributed Replicated Block Device ) is a distributed storage system for the Linux platform. It consists of a kernel module, several userspace management applications and some shell scripts and is normally used on high availability (HA) clusters. DRBD bears similarities to RAID 1, except that it runs over a network.

•  HEARTBEAT: Heartbeat is a daemon that provides cluster infrastructure (communication and membership) services to its clients. This allows clients to know about the presence (or disappearance!) of peer processes on other machines and to easily exchange messages with them. Heartbeat comes with a primitive resource manager (haresources); however it is only capable of managing 2 nodes and does not detect resource-level failures.

DRBD is often deployed together with the Heartbeat cluster manager, although it does integrate with other cluster management. It integrates with virtualization solutions such as Xen, and may be used both within and on top of the Linux LVM stack.

9 iSCSI in SAN

Till now, we have covered all the aspects of SAN but it was basically focused on AoE protocol. iSCSI has its own features and own advantages in SAN. If we need features such as encryption, routability and user-based access in the storage protocol, iSCSI seems to be a better choice. ATA disks are not as reliable as their SCSI counterparts. Therefore iSCSI can be used for SAN creation. The following table covers all the building block of iSCSI in brief: