Specifications

Escala Tower PL & S, E, T System Hardware
Chapter 3: External Storage and SAN Subsystems 39/116
9es3s1c3.doc
Rev 5.9
02/12/2003
3.11. Mirrored Caching Option
On DAS1300, DAS2900 and DAS3200/DAS3500 models, with dual SP, a cache memory is available.
Mainly dedicated to write access caching, it can be also configured as a read cache or as a read and
write cache.
The write cache drops the response time for every write access and thus alleviate the write penalty tied
to RAID5. A small amount of read cache (2 to 4 MB) will benefit sequential access.
The DAS 1000, 2000 and 3000 Series write cache is fully protected against power failures by a Battery
Backup Unit (BBU), against memory components by an ECC (Error Correcting Code) and against SP
failures by mirroring. The mirrored copy of data and associated address is saved on the second SP.
The DAS1300 can have 32, or 64 MB of cache memory. A 2 MB memory space is reserved by the SP
for internal use. DAS2900 and DAS3200/DAS3500 can have 32 or 64 MB of cache memory. A 4 MB
memory space is reserved by the SP for internal use. The actual memory capacity is twice the user size
due to mirroring protection.
3.12. Single board Caching Option
On the DAS1300, DAS2900 and DAS3200/DAS3500 models, with only
one SP
, a cache memory
option is also available. This option offers a competitive price for basic configurations.
The DAS 1000, 2000 and 3000 Series single board cache is protected against power failures by a
Battery Backup Unit (BBU), and against memory component failure by an ECC (Error correcting
Code). No mirrored copy of data is provided.
The DAS1300 can have 32 MB of cache memory. A 2 MB memory space is reserved by the SP for
internal use. DAS2900 and DAS3200/DAS3500 can have 32 MB of cache memory. A 4 MB memory
space is reserved by the SP for internal use.
3.13. Prerequisites & Configurability
The DAS 1000, 2000 and 3000 Series are available as a standard offering on the ESCALA platforms.
AIX 4.1, or later, is required.