EMC offers high-end NAS features at a mid-range price

With its Celerra NS600 network-attached storage system, EMC has pulled some of its high-end NAS technology down into a mid-range device aimed at enterprise users who want to consolidate 10 to 20 departmental and branch-office storage servers onto a single system.

Based on EMC's proprietary Unix-based Data Access in Real time (DART) operating system, the NS600 supports a number of features typically reserved for high-end NAS devices, such as extensive hardware redundancy and high-availability measures.

With its $162,00 price tag for 1 terabyte of capacity, the NS600 offers an alternative to competitive products that can cost more than $250,000.

The NS600 is a rack-mounted system with multiple components. The front end of the system is housed in the Data Mover Enclosure (DME), which has two Data Movers, each supporting six auto-negotiating 10/100/1000M bit/sec interfaces.

The Storage Processor Enclosure (SPE) supports 2G bytes of storage RAM and dual-active storage processors (2-GHz Pentium III Prestonia CPUs). The SPE manages the NS600's RAID  5 arrays, which reside in a separate enclosure. Having the Data Movers and SPE in separate enclosures ensures that if there is a disk failure, the SPE can provide the data needed to rebuild the disk without affecting data processing power within the Data Movers. In our tests, this worked as advertised.

We tested a system with 30 disks, but the NS600 can support up to 120. In addition to the RAID 5 disks, the NS600 comes with another hot spare replacement for any disk that might fail within the cabinet.

N+1 back-up power is stored in its own component (the DME and SPE each have their own dual power supplies, as well). A separate hot standby power supply for the storage processor allows data in cache to be written to a special area called a vault so that it is not lost during a system failure.

Connections between the major front-end and back-end components are via 2-gigabit Fibre Channel  links.

Fail Safe Networks (FSN) are a key availability feature on the Data Movers. They allow 10/100/1000M bit/sec Data Mover ports to be configured in redundant mode to fail over to a secondary connection if the primary connection fails. FSNs can be configured a variety of ways - in sets of two to eight ports, as Ethernet channels or in link aggregations. All connections in an FSN share a single media access control and IP address.

To test FSN, we configured Data Mover ports 0 and 1 as the primary and secondary network interfaces through a pulldown menu and then pulled the cable on port 0. The failover to secondary Port 1 was instantaneous. However, when Port 1 failed back to the primary Port 0, we observed a 49-second delay, which is high.  In our experience, instantaneous failover is optimal; more than 20 seconds is noticeable; 49 seconds is about the time we consider getting tech support on the issue.

This delay can be avoided by configuring the ports in standby mode. Once a port fails over to a secondary port, it will not fall back to the primary port (unless there is a failure in the secondary port, now acting as the primary).