Advances in Hardware RAID

March 18, 2015 | Post

Hardware RAID has been with us for quite some time and has been key in protecting local data on servers and overcoming performance barriers. Over time, hard disk interfaces have changed from the PATA and SCSI of days past to today’s ever evolving SAS pipelines. Like disk interfaces, hardware RAID controllers too have continually evolved. They don’t just bring fancy new interface speeds, but also many new advances that transform the functionality of the controllers to surface unprecedented levels of data control and performance.

Let’s take a peek at what veteran RAID vendor Broadcom has been up to in recent years and how its advances have improved common computer performance challenges.

CacheVault®: Set it and Forget It Cache Protection

RAID controllers have cache that allow you to overcome the limitations of platter-based drives by writing data to the ultra-fast RAM cache on the card. This boost in performance comes at a price: it must be protected in the event of a power interruption. Failing to do so will cause the loss of any data that was in the cache at the time but not yet committed to the disks.

For years, the solution to overcome this potential hazard has been the use of a chemical battery to provide just enough power to the RAM cache to hold the data until such time as the server can come back on line and flush the cache to disk. While an effective solution, it also requires that the battery be charged before the failure, be in good enough health to support the electrical load, and be replaced on a regular schedule to ensure safe and dependable operation (sometimes in as little as 1 year). This requires monitoring that is burdensome.

With LSI CacheVault, the battery is done away with. It is replaced instead by a ‘Super capacitor’, an electrical component that charges rapidly and does not require the maintenance nor suffer the degradation like a traditional battery might. To accommodate the relatively fast discharge time of the supercap, a CacheVault module, equipped with a small NAND flash module (like those in an SSD), is used to copy the data in the RAM cache to the NAND where it can safely reside until you get the power situation worked out. When the power does come up, the supercap is quickly recharged and ready for another power interruption. (No more waiting 12+ hours until you are protected again!)

Any modern LSI 6Gb or 12Gb RAID controller with cache is capable of having a CacheVault module and supercap added on. The module may differ depending on the controller, so always check its optional components list before employing a CacheVault module.

FastPath: Increase SSD Array Performance Up to 3X

Beyond platter-based drives, we’ve seen SSDs become a staple in the storage world, and even find their place in modern RAID arrays. As most of us know, SSDs are a different animal entirely. Sure, they can be used in place of standard hard disks, but they operate in a wildly different manner on the inside. MegaRAID® FastPath is a specialized method of addressing SSD arrays which can vastly improve performance as compared to a non-FastPath enabled controller.

FastPath is meant to take the unique characteristics of SSDs to accelerate highly random, high-volume workloads to incredible speeds, capable of increasing array performance by up the three times. While standard on their 12Gb 31xx offerings, the 6Gb offerings in the 92xx product line will require firmware level 5.7 or an optional hardware or software license to take advantage of these features. If you are running an SSD array, you should absolutely take advantage of this SSD-specific technology to boost your performance.

Secure Data with SafeStore

Data security continues to be a hot topic. With sensitive data handling and storage comes the need for encryption. Many disks have standalone, disk-based or software-assisted encryption, but when using disks in an array, key management and repurposing can be time consuming and prone to mistakes. LSI MegaRAID SafeStore is an optional component which enables the controller to act as a key storage device for all of the attached disks. It also provides an Instant Secure Erase feature which will ‘forget’ the encryption keys, effectively rendering the data on the disk unrecoverable. This can decrease drive disposal or repurposing time while keeping everything manageable from a single interface.

The feature is available as a software or hardware license on the majority of the 6Gb and 12Gb controller lines.

CacheCade®: Get Blistering Performance, but Keep the Capacity

Now for the fun stuff. So you have the need for a high capacity data array but you have some ‘hot’ data that needs fast servicing. You have some options:

  1. You create a large storage array and a smaller SSD array, write an algorithm to detect frequently requested data that will move said data to the SSD array, and create the appropriate pointers to it so the requesting software understands it.
  2. Do the same thing, but find some third party software to do that bit and trust it interprets the file system statistics correctly (and still create the pointers so the requesting software understands).
  3. Create a very expensive, all SSD array to overcome your problem.

Might I recommend a number 4? Try LSI MegaRAID CacheCade.

LSI CacheCade is an interesting optional feature compatible with many 6Gb and 12Gb LSI RAID controllers which can incorporate a couple of SSD drives to do exactly what is trying to be done above. Instead of bogging down the controller with managing multiple arrays and incorporating software tools and filesystem hacks to get the job done, CacheCade provides a transparent interface which will (from the RAID controller’s own internal statistics) copy the ‘hot’ data to the SSD array when necessary, all while your filesystem is none the wiser. To you or your end user, frequently accessed data is simply served up at blistering speeds while you retain your large, mechanical, high-capacity array. This solution allows for cost-effective performance improvements, all from a managed and transparent angle.

To get the most from CacheCade, you are going to want to make sure that your workload is one that makes sense for this sort of data tiering. If your workload only uses data one or two times before discard or cold storage, or if you have a constant churn, such as in line speed network capture or pure video ingest, this might not be the ideal solution for you. However, if you are hosting content, or perhaps administering a database from the system in question, you could potentially reap huge performance benefits.

I should remind potential users of high data turnover systems that may still benefit from CacheCade to be vigilant about properly specifying SSDs of suitable endurance. High data turnover could mean high volumes of writes, potentially exhausting the NAND on your SSDs. Choices then have to be made to either invest upfront in high drive-writes-per-day disks, or to expect regular replacement. While this won’t apply to every user of CacheCade, endurance must always be considered as a factor when creating the specification for a given application server.

CacheCade modules are available for the majority of the 6Gb and 12Gb LSI RAID controller line. CacheCade 2.0 has a capacity limitation of 512GB, so be sure to consider that as well when determining your server specification.

Cache Coherency with Syncro

I wouldn’t say that high availability systems have been struggling with the issue of controller write cache coherency, but that’s only because you simply can’t afford to leave it on. With multiple RAID controllers in the mix on a high availability direct-attached storage solution, having a volatile cache in play will certainly mean not only data loss if a node goes down, but also a synchronization loss issue. What’s the point of HA if you don’t have complete sync between nodes?

Enter LSI Syncro, a pair of RAID controllers, bound with a software framework to allow complete cache coherency across both cards. True hardware HA storage, all in a turnkey package that is ready to drop into your solution. By allowing both cards to ‘share’ cache information, either card can be interrupted, simply to have the other pick up where the first left off. Syncro does require the purchase of a kit which includes the pair of controllers as well as the CacheVault modules necessary to protect against a total power loss. Current offerings come in both 6Gb and 12Gb in the form of the CS 9271-8i and CS 9286-8e for your 6Gb internal and external needs, respectively, and the Syncro 9361-8i and Syncro 9380-8i for your 12Gb needs.

Final Thoughts

While we are talking about RAID, it should be mentioned that for deep capacity needs, most modern RAID controllers can address many, many more drives than for which they have the physical ports. Using a SAS expander (either backplane or standalone card), a 9361-4i 4-port controller, for example, can address as many as 128 disks. This can be useful for cascading out to multiple chassis to maximize array density.

I’d also like to mention the importance of using a quality controller, even when utilizing software-defined storage solutions. Using a low quality controller can impede the performance and reliability when using filesystems like ZFS, or the various object storage solutions. And Broadcom offers a full line of high quality HBA products that can fit any deployment design, even if hardware RAID isn’t in the cards.

MBX Systems

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