IBM claims that it has shipped over 5,200 XIV Storage Systems and 384 petabytes of capacity since it acquired XIV in 2008. The product is targeted to big data, virtualized data centers, and cloud deployments.
An XIV Storage System consists of modules, each containing a multi-core CPU, RAM, and disk drives, that work in parallel to service I/O. Each module is linked with InfiniBand, and software running on the modules allows each to act as an independent storage system and handle its own caching and snapshots.
With the addition of an SSD cache, the company also claims that the XIV can perform at 160,000 I/O per second with 180 disk drives and 79 terabytes of capacity.
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In IBM's implementation, the SSDs are used as a secondary cache between the hard disk drives and the DRAM cache. Data is always placed in both cache units and disk access is avoided when data resides in the SSD cache. The SSD cache needs to be at least an order of magnitude bigger than the DRAM cache to be effective.
In host reads, the XIV checks for data in SSD cache. It a hit is made, it re-routes the requests to the SSD for quick retrieval of the data. If not hit, it forwards the requests, unmodified, to the drives. Upon return, it copies the pages into an internal buffer. When the buffer fills up, it is de-staged to the SSD, sequentially, and sequential I/O detection bypasses the SSD to avoid cache poisoning.
In host writes, all writes go to the DRAM cache, and as they are de-staged from the cache, they are synchronously staged onto the SSD buffer. When the buffer is full, the data is written to the SSD.
The SSD cache, available on all Gen3 XIV systems, consists of a 400-GB SSD on each module and 6 TB of cache per rack. The SSD is housed in a PCI caddy in the rear of the module and can scale from 6 to 15 SSD drives.
The company also added the ability to mirror data between previous XIV storage systems and the new Gen3 systems. This allows customers to migrate data off old arrays and onto the new arrays and to then repurpose their older XIVs as disaster recovery backup systems.
IBM also added to the remote monitoring capabilities of the XIV by allowing iPhone users to manage the systems from anywhere. The app will be available for free download later this month. IBM previously released the XIV Mobile Dashboard for iPad users last year.
The company also promised IPv6 support in the first half of this year, followed by USGv6, the government implementation of IPv6, later in the year.
Deni Connor is founding analyst for Storage Strategies NOW, an industry analyst firm that focuses on storage, virtualization, and servers.
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