Originally posted by: Snig
I have been having some discussions internally about cache and the destaging of cache to disk, so I thought I would post some questions here and get the answers from the guru's themselves. This thread will start with the basics and will eventually walk a write IO though it's lifecycle to the backend disk. I then want to expand it into striping and discuss software RAID0 over hardware RAID5/RAID1 and go from there. I told you it would be the ultimate. ;-) Pictures or PPT slides would be sweet.
All of this will pertain to a Unix host attached to USP1100 using 146GB/10K drives in a 7+1 RAID 5 configuration. The Unix host is using 64K stripes for it's file system. The disk subsystem is carved up into 14GB LDEVs using the OPEN-V emulation.
So here is my first set of questions:
- A cache slot is made up of cache segments. For an Open-V device how big is a cache slot? How many segments per slot?
- A cache segment is made up of cache blocks. How big is a cache segment? How many cache blocks in a segment?
- A cache block is made of Subblocks. How big is a cache block? How many Subblocks are in a block? How big is a subblock?
- Assuming that a full 64K write comes into cache from the host,is it accepted in as the full 64K or broken into something smaller? If smaller, how is that broken up?
- How big are the stripes to the backend disk when destaged from cache?
That's good for now. We'll move on once we have these answers.