Dell EqualLogic iSCSI SAN Storage Pricing Performance Virtualisation VMware

Overview The PS in PS Series stands for Peer Storage - to quote the EqualLogic website - "peer means collaboration and equal partnership in a single, simple architecture - components and arrays work together to share resources, distribute loads and collaborate for maximum performance, total data protection and seemless scaling."

In simple terms each EqualLogic iSCSI SAN device is a self-contained, fully redundant appliance with no single point of failure. Each PS Series (PS4000, PS5000, PS6000) appliance contains sixteen hard disk drives which can be either SATA2, 10K SAS or 15K SAS. Storage is virtualised, which means that all drives within the array(s) work together to form a storage pool, from which individual volumes can be presented. This results in exceptional performance, and "five 9's" reliability. Within each appliance hot spares are automatically allocated and the remaining disks can be deployed as RAID 10, RAID 50, RAID 5 or RAID 6 depending upon performance or capacity requirements. It is even possible to "hot-migrate" from one RAID level to another without any interruption to service (RAID10->RAID50->RAID5).

Pool-Based Approach Much Like a VMware virtual environment, multiple appliances can be simply combined to increase the size of the storage pool, and because each appliance contains additional controllers, cache and network interfaces, performance actually scales upwards in an almost linear fashion. Traditional SAN design involves specification of single or dual controllers, with performance gradually diluted as additional shelves of disk are introduced. Adding additional appliances to an EqualLogic storage pool actually increases performance and resilience. Different combinations of disk and RAID level can be mixed within a multi-appliance storage pool to provide a combination of performance and capacity - with intelligent algorithms managing distribution of data at block level within the array to ensure that performance hungry applications can access their data quickly, whilst archive data does not clutter up the more expensive, faster disk.

Simple Management One of the key selling points of the PS Series is the simplicity of deployment and ongoing management. All tasks are completed through a simple web interface which provides full control of all appliances within a pool. A features are administered from this point - snapshots, replication, thin provisioning, grouping, scheduling etc. It cannot be stressed enough how straightforward this is - it is entirely possible to be presenting volumes to servers within 20-30 minutes of power-up - try that with a traditional fibre-channel SAN!

iSCSI The iSCSI standard has emerged as a cost-effective alternative to Fibre Channel in recent years. Following some initial scepticism the standard is being widely embraced at all levels, based upon proven performance and reliability. Because iSCSI utilises a familiar ethernet infrastructure, no specialist skills are required beyond those that you should already have in-house. iSCSI host bus adapters (HBA's) are available, the free iSCSI initiator provided with almost alll operating systems, in conjunction with Gigabit or 10GbE NIC's provides ample performance.

It is important to mention that the EqualLogic appliances were designed from the ground up with iSCSI in mind, which is why they occupy their class-leading position. Many other iSCSI appliances are actually based upon fibre channel architecture with an iSCSI interface "bolted on". The translation between this interface and the back end adds additional overhead which inevitably has a performance cost.

The PS Series also has an innovative fully-inclusive licensing model, which contributes to the exceptional value offered by this platform - this is covered elsewhere on this site.

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