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тАО07-17-2009 01:27 PM
тАО07-17-2009 01:27 PM
1)What is the difference between cache memory and shared memory on XP12000?.
2)Please explain the detailed write operation on XP12000.
3)Please explain the detailed read opearation on XP12000.
4)What read and write policies are used for the cache memory?.
Thanks
Solved! Go to Solution.
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тАО07-17-2009 08:32 PM
тАО07-17-2009 08:32 PM
Re: XP12000 cache memory and shared memory
this could help you:
http://h71028.www7.hp.com/ERC/downloads/4AA0-7923ENW.pdf?jumpid=reg_R1002_USEN
CACHE MEMORY page 18
Cache memory is used to transfer data between the host CHIP processors and the ACP disk controllers. In fact, cache memory is an integral part of the data path, as all data is transferred through cache before being transferred between the disk and the host server. Cache is also mirrored, allowing all write data to be written in cache twice, one time each on two separate battery-backed-up cache platform boards.
SHARED MEMORY page 20
Shared memory is independent of the cache memory and is used to store tables and other information used for disk management, thus freeing up the cache memory for user data. Shared memory is also used to store system configuration information. The configuration information includes system component mapping, LUN maps, cache pointers, and RAID levels.
Sequential and Random IO workloads from page 9
...
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тАО07-18-2009 07:53 AM
тАО07-18-2009 07:53 AM
Re: XP12000 cache memory and shared memory
Thanks again.
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тАО07-18-2009 09:34 AM
тАО07-18-2009 09:34 AM
Re: XP12000 cache memory and shared memory
XPs are cache centric storages
Writes and Reads
the CHIP (Front end controller) writes data into both cache areas (duplex) to avoid that data will be lost if a cache error occurs when it is not yet written on the disk.
The shared memory is used to classify and control the data in cache according to its attributes (enqueue/dequeue)
Write data (new data) and read data (old data) are handled in separate segments, thus not overwritten - write penalty compensation.
Read data (parity included) is
staged into either cache A or cache B
If the write data causes a cache miss, the data of the target record up to the end of the track is staged into a read data slot
and the write data is transferred.
If there is a cache miss of the parity data, the old parity is staged into a read parity slot.
When all necessary data for generating new parity is there, it is transferred to the memory of the DKA (disk controller)
After the new parity completion, the DKA memory duplexes it into both write parity slots of the cache and it is ready for the destage
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тАО07-20-2009 06:41 AM
тАО07-20-2009 06:41 AM
Solutionpp 11-15 of the below document are dedicated to Cache Memory and Shared memory on the XP24000. The principles are the same on the XP1200 although max cache installed etc will be lower on the XP12K.
This covers ,uch of what IBalty has said but may be in more detail. Anything more than what is included in my doc and what IBalty has said is probably Hitachi confidential.
http://blogs.rupturedmonkey.com/wp-content/uploads/2009/04/usp-v-unofficial-manual-v0003.pdf
PS. Its a bit rude not to assign points to the responses above.
Nigel
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тАО07-20-2009 08:26 AM
тАО07-20-2009 08:26 AM
Re: XP12000 cache memory and shared memory
Thanks a million.
P.S: I never knew there was a point system. I thought the moderator assigns the points. Please pardon my ignorance.
thanks again.