HSZ70 HSOF 7.2, 7.7
Tru64 4.0D
All of our stripesets and striped mirrorsets have a chunk size of 256
blocks, the default.
Is anybody using the new recommended chunk size of 157, 239, or 317 blocks
for an 8 KB request size? Specifically for Oracle on AdvFS for an OLTP
application (SAP R/3). Anybody using the chunk size of 17 for storagesets
that are accessed sequentially, such as for the Oracle archived redo logs
files?
We have a new HSZ70 array to add and new storagesets to configure.
The original documentation for the HSZ70 (and the HSZ50) recommended that
the default chunk size of 256 blocks (= 128 K) for a stripeset or RAIDset
with 9 or less members be used and warned against using an improper chunk
size.
The new documentation advises that the default chunk size should be used
with caution and recommends that in order to increase the request rate, a
chunk size of 10 to 20 times the average request size, "rounded" to the
nearest prime number, be used:
* If there is a lot of parallel I/O on a small area of data, use a chunk
size that is 10 times the average request size.
* If the areas being accessed are scattered, use a chunk size that is 20
times the average request size.
* If you don't know, use a chunk size that is 15 times the average request
size.
Therefore, for an 8 KB request size, the documentation says to use a chunk
size of 157 for high locality, 239 for unknown locality, and 317 for low
locality access. (Chunk size is in disk blocks = 512 bytes.)
To increase the data transfer rate, the updated documentation says that a
chunk size of 17 generally works well for sequential access on stripesets.
Joe Ledesma
Oracle DBA / SAP R/3 Basis / UNIX Admin
Sacramento, CA USA
Received on Fri Jul 21 2000 - 00:16:24 NZST