Nimble Storage’s Cache-Accelerated Sequential Layout (CASL)
is the foundation for its high performance, capacity efficiency, integrated
data protection, and simplified lifecycle management of its storage systems.
CASL accelerates applications by using flash as a read cache coupled with a
write-optimized data layout. The CASL architecture includes features such as
flash-based dynamic cache, which accelerates read access to application data by
holding a copy of “hot” active data in flash, and a write-optimized data
layout, in which data written by a host is first coalesced, then written
sequentially as a full stripe to a pool or disk. Other features of CASL include
efficient integrated replication, inline universal compression, instantaneous
point-in-time snapshots, and zero-copy clones.
Architectures that use a write cache to accelerate writes
are often confused with the CASL architecture, which accelerates write
performance using a sequential layout. Though both of these may have some
similarities at first glance, many people miss the key elements that
differentiate CASL from other architectures on the market.
The purpose of CASL is to accelerate back-end disks by
turning random IO into sequential IO. Nimble’s CASL architecture has no
predetermined mapping of logical block addresses (LBA) to physical locations or
block boundaries with CASL’s support for variable block sizes. CASL does not
rearrange blocks; it simply constructs a large set of blocks into a large
physical stripe, reducing all random write operations into one. Unlike traditional storage architectures,
Nimble’s CASL write performance is not limited by disks and write caches but by
the CPUs compressing and decompressing data.
Traditional storage architectures use LBAs, which uses a map
of predetermined physical locations on a disk. Data is written to disks as
quickly as possible, but random, non-sequential writes have increased latency
over sequential writes resulting in larger write latency. Combined with the
need to read data from the same disk drives, read performance is decreased more
as a disk tries to balance finding requested data and writing incoming data.
Nimble Storage is revolutionizing data storage with the CASL
architecture by leveraging the unique properties of flash and disk to deliver
high performance and capacity with the only flash optimized solution.