Wednesday February 09, 2005
Wednesday February 09, 2005
Content Addressable Storage (CAS) CAS is an interesting new approach to storage [well actually it's been around a while, just not broadly commercialized] where a crypto hash "checksum" is calculated for every file that's stored. The hash algorithm might be the lately maligned 80-bit MD5 or a 160-bit SHA1 or something different. The adjective "Content Addressable" is relatively misleading since it implies that the hash is used as a file handle. Yet there are no systems that work like that today, including Centera for which the CAS acronym was invented. Filepool, Scale8, and a variety of other researchy SSP-oriented storage designs did use hashes for internally-facing file handles, but none of those things are commercially deployed today afaik.
Why use hashes? Well the real reason is that it simplifies the design for a storage system intended to be scalable by eliminating the need for distributed lock management across a clustered system. The serendipitous benefit is that it typically means objects are immutable, something useful for SEC-regulated applications.
So the term CAS is not particularly accurate, is aligned pretty strongly with EMC, and is not particularly benefits oriented so their term will die a slow death over the next couple years. In fact SNIA has already changed the naming of their respective committee away from CAS.
For file handles...
So CAS is a loose term for things for things that
a) are WORM systems and
b) calculate a hash somewhere along the way.
Trackback URL: http://blogs.sun.com/m/entry/content_addressible_storage
Comments:
Post a Comment:
| Archives | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Language | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Links | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Referrers | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Today's Page Hits: 82 |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
