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SSD Cache, Snapshot and Drive Encryption for RAID

Original Article Date: 2010-09-28 

2010 has been a busy year for RAID (Redundant Array of Inexpensive Disks), the storage sub-system that lies at the heart of servers. A number of new developments have accumulated in this area to justify putting together a technical update.

Here's a summary of what I'll be covering:

  • The transition from 3Gbps to 6Gbps per channel in both SATA and SAS.
  • Optimization for Solid State Drives (SSDs) in RAID, and the use of SSDs as huge data caches for conventional hard drive RAIDs.
  • Ability to create snapshots at the RAID volume level for additional data recovery.
  • Protecting sensitive data through self encrypting drive support.
  • Saving slot space in rack servers through low-profile RAID modules.

All these developments come through on the new line-up of Intel-branded RAID controllers, which have just become available.

Transitioning to 6Gbps

Since the introduction of SATA and SAS some years ago, we've been quite content with the 3Gbps (gigabits per second) limit on each drive channel. This is because these technologies are a point-to-point connectivity (one physical hard drive per port), and conventional hard drives have never been fast enough to break the 3Gbps limit. But with the advent of SSDs, sustained data rates of greater than 3Gbps are proven, and also improved caching on conventional SAS drives has made it possible that the 3Gbps limit may be exceeded for short bursts where repeated data is accessed multiple times.

6Gbps capability started rolling out on RAID controllers about a year ago, with hard drives and SSDs appearing with the new standard in the last few months. These products are indicated as "6Gbps", "SATA-III" or "SAS 2.0" so you will be able to distinguish them from the older 3Gbps standards (SATA-II and SAS).

Optimization and Caching with Solid State Drives

The appearance of Solid State Drives (SSDs) a couple of years ago heralded great change in computer storage. With no mechanical parts, reliability and shock resistance is superb, sustained data transfer rates are higher, but most important of all, seek times are orders of magnitude less than conventional drives. However, SSDs still have a significant price premium, being many times costlier per GB than conventional drives. Eventually this will change, once SSD technology becomes mainstream, but this may still be many years away.

SSDs can provide significant enhancements to RAID, if used intelligently.

SSDs can be used exclusively to build all-SSD RAIDs. But the cost per GB currently limits this configuration to all but the most demanding applications. Also, existing RAID controllers are not optimised for SSDs, whose I/O profiles significantly differ from conventional drives. These two factors have discouraged the building of all-SSD RAIDs up to this time. However, Intel have released a special module that can be added to some of their new 6Gbps RAID controllers. Called FastPath I/O, this feature comes included with one of the new Premium Feature Keys (small chips that are physically plugged into the RAID controller card), and modifies the I/O instruction set of the RAID controller to work best with SSDs.

The most advantageous use of SSDs in RAID at this time, however, is in providing an extended middle-tier cache in powering arrays with large capacity conventional hard drives. RAID controllers have incorporated DRAM based caches for many years, but have usually never exceeded 512MB in size. It has been found, however, that extending the size of the RAID cache to several GB has provided dramatic improvements in RAID performance, especially in database and other applications where re-use of data is common.

SSDs, which fit somewhere between DRAM and conventional HDDs in terms of price per GB and speed, have found themselves to be the perfect candidate for providing such an extended cache. Adaptec was the first to offer such an arrangement with their MaxIQ RAID SSD Cache Kit. Intel, however, have followed suit, now offering SSD Cache capability with the same Premium Feature Key that also includes all-SSD RAID Optimisation (discussed in the above) for use in some their new 6Gbps controllers.

Maximum Data Recovery through RAID Snapshot

Most IT administrators will be familiar with backup software that allows the taking of drive volume "snapshots", whereby the system is either backed up routinely every hour or every day, or manually prior to doing some driver or system updates that may affect system stability. These software applications, obviously, sit on top of the OS, and so in the event of the corruption of the OS itself, a rescue disk becomes necessary, which can be inconvenient in terms of loading drivers etc.

What if you could make volume snapshots at the RAID level, though? In that way, should an OS get so corrupted that it could not re-load, you could simply enter the RAID BIOS and restore the last working snapshot. Additionally, such a utility could be completely independent of any OS, and the need for rescue disks etc. Well, with Intel's Rapid Recovery Snapshot Premium Feature Key for select Intel 6Gbps RAID controllers, such functionality becomes possible. Within the RAID administrator software (which can be either installed on top of the OS, or used within the RAID BIOS), the IT admin can make snapshots of the entire RAID volume, and then reload such snapshots later in the case of difficulty. A handy feature indeed!

Bulletproof Protection of Sensitive Data with Drive Encryption Management

Losing sensitive data on your hard drives can be costly, embarrassing and even possibly have legal consequences. With the last of Intel's Premium Feature Keys for their new 6Gbps RAID Controllers, called Drive Encryption Management, your drives can be locked to that particular RAID controller, so that if the drives are removed for repair, replacement, retirement, or are stolen, then the data is unreadable. This is because, with this Premium Feature Key added, the RAID controller does a full AES 128-bit encryption with every I/O operation. The only requirement is that the drives are SEDs (Self-Encrypting Drives), which are available as special models from all leading hard drive manufacturers.

Summary of Intel RAID Premium Feature Keys

A number of the new 6Gbps RAID controllers from Intel have the capability of adding one of three Premium Feature Keys (PFKs), which are small chips that slot onto a receptacle located on the controller card. Only one of each key can be used on any single controller. In summary, these are:

  • AXXRPFKSSD: SSD Cache and FastPath I/O, for both SSD Caching supporting conventional HDDs, plus all-SSD RAID Optimization
  • AXXRPFKSNSH: Rapid Recovery Snapshot, for making snapshots of the entire RAID volume, for rapid recovery in the event of trouble
  • AXXRPFKDE: Drive Encryption Management, for protecting your most sensitive data in the event of a drive being stolen or being retired

These PFKs are listed under the "RAID Enhancements" section of all our server and workstation configuration pages. RAID controllers that support these products are listed with "PFK" in their description.

Saving Slot Space in Rack Servers with Low-Profile RAID Modules

In 1U rack servers, PCI slot space is often at a premium. Some 1U server barebones (dedicated chassis with motherboard) have a double-sided riser card that allows for a full height PCI card on one side, with usually a half-height card permitted on the other. So at most you have two slots. Intel have a range of daughter-board type modules that plug into special slots on their server boards. These modules either provide additional LAN ports, or full-fledged RAID, without taking up those valuable PCI slots. You will find options for such RAID modules listed as options with our Intel-based rack servers, such as the CAPELLA and SIRIUS models.  


So there's been quite a refresh in the world of RAID.

  • Moving to the new 6Gbps per port bandwidth will future proof your controller against any new drives that should appear for the next 5 years
  • Low profile RAID modules provide fully fledged RAID while preventing valuable PCI slots on 1U and 2U servers from being used up
  • SSDs are finally embraced by providing massive middle-tier caching capability for conventional hard drive arrays, as well as now being catered for through full optimization of all-SSD RAIDs
  • The RAID volume itself can be backed up and restored within the RAID BIOS
  • Sensitive data is protected on drives that must be retired or replaced by locking them to the controller itself

Isn't it time for you to revisit the world of RAID and see what it could do for you?

Best regards,

Ben Ranson
Chief Systems Engineer
Electronics Nexus