IBM SAN Volume Controller - Features (2012)

Features (2012)

Indirection or mapping from virtual LUN to physical LUN

Servers access SVC as if it were a storage controller. The SCSI LUNs they see represent virtual disks (volumes) allocated in SVC from a pool of storage made up from one or more managed disks (MDisks). A managed disk is simply a storage LUN provided by one of the storage controllers that SVC is virtualizing. The virtual capacity can be larger than the managed physical capacity, with a current maximum of 32 PB, depending on management granularity (extent size)

Data migration and pooling

SVC can move volumes from one capacity pool (MDisk group) to another whilst maintaining I/O access to the data. Write and read caching remain active. Pools can be shrunk or expanded by removing or adding hardware capacity, while maintaining I/O access to the data. Both features can be used for seamless hardware migration. Migration from an old SVC model to the most recent model is also seamless and implies no copying of data.

Importing and exporting existing LUNs via Image Mode

"Image mode" is a non-virtualized pass-through representation of an MDisk (managed LUN) that contains existing client data; such an MDisk can be seamlessly imported into or removed from an SVC cluster.

Fast-write cache

Writes from hosts are acknowledged once they have been committed into the SVC mirrored cache, but prior to being destaged to the underlying storage controllers. Data is protected by replication to the other node in an I/O group (node pair). Cache size is dependant on the model of SVC used. Fast-write cache is also used to increases performance in midrange storage configurations.

Auto tiering (Easy Tier)

SVC automatically selects the best storage hardware for each chunk of data, according to its access patterns. Cache unfriendly "hot" data is dynamically moved to solid state drives SSD, whereas cache friendly "hot" and any "cold" data is moved to economic spinning disks.

Solid state drive SSD support

SVC can use any supported external SSD storage device or provide its own internal SSD slots, up to 32 per cluster. Easy Tiering is automatically active when mixing SSDs with spinning disks in hybrid capacity pools (MDisk groups).

Thin Provisioning

LUN capacity is only used when new data is written to a LUN. Data blocks equal zero are not physically allocated, unless previous data unequal zero exists. During import or during internal migrations, data blocks equal zero are discarded (Thick-to-thin migration).

Besides, thin provisioning is integrated in the FlashCopy features detailed below to provide space-efficient snapshots

Real-Time Compression

This technology, invented by the acquired startup Storwize, has been integrated in the SVC and other IBM storage systems. Originally implemented as real-time file compression, it has since been enhanced to also support in-flight block compression. The efficiency is equal to "zip" LZW (Lempel–Ziv–Welch) with a very large dictionary. The temporal locality of the algorithm may also increase the read/write performance on adequate data patterns such as uncompressed databases stored on spinning disks.

Real-time compression can be combined with Easy Tiering, Thin Provisioning and Virtual Disk Mirroring.

Virtual Disk Mirroring

Provides the ability to make two copies of a LUN, implicitly on different storage controllers

Site protecion with Stretched Cluster, also called Split IOgroup

A geographically distributed cluster layout leveraging the virtual disk mirroring feature across datacenters within 300 km distance. A stretched cluster presents one logical storage layer over synchronous distances for increased high availability. Unlike in classical mirroring, logical LUNs are writable on both sides (tandem) at the same time, removing the need for "failover", "role switch", or "site switch". The feature can be combined with Live Partition Mobility or VMotion to avoid any data transport during a metro-distance virtual server motion.

Each side's SVC nodes also have access to the other side's physical storage hardware, removing the need for site-resynchronization in case of a simple node failures.