Fail-in-place systems: Avoiding hard disk drive failures

Fail-in-place is a fairly new concept aimed at resolving some of the side effects of hot-plug or hot-swap hard disk drives (HDDs) in storage systems. Examples of these difficult side effects include pulling the wrong drive and causing inadvertent data loss; delaying the replacement of a failed HDD, which defers rebuild starts and increases data loss risk; or using spare drives that may not have been recently tested, which may result in a second hard disk drive failure.

The basic concept of fail-in-place is to redefine and increase the smallest field-replaceable unit (FRU) from being a HDD to being a storage pack. A storage pack is a collection of hard disk drives operating in concert with a certain percentage of capacity allocated for sparing. Hard disk drive failures are automatically rebuilt from the allocated capacity. There are currently only two vendors supplying fail-in-place storage systems: Atrato Inc. (with its Velocity1000 or V1000) and Xiotech Corp. (with the Emprise 5000 or ISE). Both systems feature end-to-end error detection and correction, as well as autonomic self-healing.

Both vendors' product architectures are based on the concept of available user capacity being tightly coupled with enclosure lifecycle within a single FRU. An enclosure's lifecycle is the timeframe in which the enclosed raw capacity will be available to an application. The total enclosure capacity also includes an allowance for anticipated sparing requirements over the warranted capacity life of the enclosure (three years for Atrato and five years for Xiotech).

Atrato V1000 vs. Xiotech Emprise 5000 or ISE

The differences between the two implementations are reflective of each vendor's product philosophies. Atrato makes 2.5-inch SATA drives enterprise-capable with their ORT, end-to-end error correction and detection, autonomic self-healing, high densities per enclosure, and with clever vibration and cooling methods. They improve performance by combining 160 drives for up to 80 TB in a 3U enclosure that provides up to 12,500 IOPS and 1.5 GBps throughput from a single enclosure.

Xiotech's focus is on providing increased reliability and performance from enterprise Fibre Channel and SAS 3.5-inch and 2.5-inch drives. The baseline FRU is a sealed DataPac of 10 3.5-inch or 20 2.5-inch Fibre Channel or SAS HDDs for up to 16 TB in 3U. Each ISE has dual removable DataPacs, power supplies with cooling, 96-hour battery backup and active-active RAID controllers.

Unlike standard storage subsystems, ISE DataPacs feature innovations such as sophisticated vibration reduction and improved cooling; Xiotech exploits the internal structure of all of the components to fully leverage very advanced drive and system telemetry. DataPac drives feature special firmware that relieves the burden of device compatibility required of all other storage subsystems. The result of the tightly knit control within the DataPac is a highly reliable "super disk" that has demonstrated more than a 100-fold increase in reliability vs. a typical storage system drive bay (based on Xiotech's test of 208 ISEs containing 5,900 drives for 15 months with no service events).

Atrato and Xiotech have proven that fail-in-place works. Their product testing indicates these technologies can virtually eliminate HDD replacement service calls, which translates into lower costs, less risk of lost data and fewer application disruptions.