From: RichGlazier@netscape.net
Date: Fri Dec 20 2002 - 21:04:58 EST
Managers,
I am looking for information on the relationship between the various "buckets" my write operations encounter. I am runing Oracle 8.0.6.3 on a v5.1 PK5, 3 node GS80 cluster using AdvFS (i.e. no DIO enabled) *phew*. The Oracle block size x block counter is such that Oralce is writing in 128K chunks. All of my AdvFS file domain's write blocks sizes are 256 (128k). They are writing to 0+1 storageset on an HSG80 that have a default stripeset chunksize of 256 (128k). This looks to be a streamlined operation, in that a single I/O operation won't span multiple advfs "chunks", or multiple disks in the stripeset (i.e. one disk will satisfy the write). If this is incorrect thinking, please let me know. My real question is, where does MAX_READ_CACHED_TRANSFER_SIZE and MAX_WRITE_CACHED_TRANSFER_SIZE fit into the equation? It would make sense that I would want these to also be 256 blocks (128k) or higher, so that now the application can do one write to cache, and the controller can do one write from cache to disk.
Is it safe to say that if I had this value twice as large as the average I/O (i.e. 512 blks), that for each new write to cahce, the last write to cache gets written to disk? What is the benefit to this? Is it that a slow disk can look faster to the OS because more writes are getting satisfied by the cache than are actually getting written to disk? I don't know if I want Oracle thinking there are too many writes commited that really arn't committed to disk, in case the DB goes toes up. And where does tuning MAX_CACHE_TIMER come into play? Sorry for all my thinking out loud.
The bottom line is: The controller sets MAX_READ and MAX_WRITE to 32 when you create a unit. Why? sys_check suggests a value of 256. Why? Is this because all my domains are 256?
Here is how I see the flow of I/O (without getting into UBC or all the other AdvFS buckets):
Oracle ---> (UBC) --> AdfVS ---> UNIT cache ----> Storageset chunk128k 128k 128k 128k
Any other AdvFS or HSG80 tuning I should consider?
As a side note: How does sys_check grab my HSG80 unit info? I don't have SWCC enabled on this unit, and there is no serial connection to the HSG80. Does it use hsxterm5? I'm only curious.
Thanks in advance.
Rich Glazier
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