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18 DS6000 Series: Concepts and Architecture
1.3.4 Use with other virtualization products
IBM TotalStorage SAN Volume Controller is designed to increase the flexibility of your storage
infrastructure by introducing a new layer between the hosts and the storage systems. The
SAN Volume Controller can enable a tiered storage environment to increased flexibility in
storage management. The SAN Volume Controller combines the capacity from multiple disk
storage systems into a single storage pool, which can be managed from a central point. This
is simpler to manage and helps increase utilization. It also allows you to apply advanced Copy
Services across storage systems from many different vendors to help further simplify
operations.
Currently, the DS4000 series product family (FAStT) is a popular choice for many customers
who buy the SAN Volume Controller. With the DS6000 series, they now have an attractive
alternative. Since the SAN Volume Controller already has a rich set of advanced copy
functions, clients were looking for a cost efficient but reliable storage system. The DS6000
series fits perfectly into this environment since it offers good performance for the price while
still delivering all the reliability functions needed to protect your data.
The SAN File System provides a common file system for UNIX, Windows, and Linux servers,
with a single global namespace to help provide data sharing across servers. It is designed as
a highly scalable solution supporting both very large files and very large numbers of files,
without the limitations normally associated with Network File System (NFS) or Common
Internet File System (CIFS) implementations.
To be able to share data in a heterogeneous environment the storage system must support
the sharing of LUNs. The DS6000 series can do this and thus is an ideal candidate for your
SAN File System data.
1.4 Performance
At the time this redbook was written, no officially published performance benchmarks were
available.
With its fast six processors on the controller cards and the switched FC-AL disk subsystem,
the DS6000 series is a high-performance modular storage system.
Some other performance relevant features are discussed in the following sections.
1.4.1 Tagged Command Queuing
Tagged Command Queuing allows Multiple AIX/UNIX I/O commands to be queued to the
DS6800, which improves performance through autonomic storage management versus the
server queuing one I/O request at a time. The DS6800 can reorder the queue to optimize disk
I/O.
1.4.2 Self-learning cache algorithms - SARC
Cache algorithms determine what data is stored in cache and what data is removed. Read
ahead caching will not store recently used data in cache, but will pre-fetch data and load it
into cache. This is based on the idea that the application will want the next chunks of data in
addition to the data it just received.
Most vendors use a cache algorithm based on what is commonly known as Last Recently
Used (LRU), which places data to cache based on server access patterns. IBM's patent