why md request buffers will not across devices
hi,
I have a silly question. Why md request buffers will not across devices? That means Why a bh will only locate in a single storage device? I guess maybe file system has aligned the bh? Who can tell me the exact reasons? Thanks a lot!
zkwang
Quoted 6 lines · On Wednesday January 18, [email protected] wrote:
hi,
I have a silly question. Why md request buffers will not
across devices? That means Why a bh will only locate in a single storage device? I guess maybe file system has aligned the bh? Who can tell me the exact reasons? Thanks a lot!
If you are talking 'bh' then you are talking '2.4'.
In 2.4. all requests match the 'blocksize' of the device (typically 1K or 4K) and are aligned to that size. As the chunksize is always a multiple of the block size a block will never cross a chunk boundary and so never cross a device boundary.
2.6 is quite different and md sometimes needs to split a 'bio' request to feed part to one device and part to another.
NeilBrown