I think part of that message got clipped. > From looking at the io-cache.c source, it's not clear that the entire > file would be cached, byte ranges of heavily accessed portions of > those files, or what. Also, you can't specify a storage device to use > as a cache target like /dev/sdb1 so I have to assume it reserves some > memory and then keeps the cached files there. > > This brings me to three questions: > > 1) In order to use the SSD device would I create a really large swap > file on the SSD device and then allocate the size of the SSD to > IO-Cache? Because I'm not that familiar with memory caching I'm > wondering if the calls it makes to place data it wants into memory > would stop at the point the system begins to swap, no matter what > number I provide. In this case, because of the SSD speed I don't want > it to stop at the system begins to swap. Swapping becomes a good > thing. > > 2) Would IO-Cache attempt to cache the entire 2GB to 400G file, > skipping those over my IO-Cache allocation size (lets say 60G) or > would it just cache the byte ranges of the most heavily accessed parts > of those files? For instance, if someone is running a database server > within one of the qcow2 files would and is hitting the "foobar" table > with selects really hard, would IO-Cache cache the data being > referenced (inodes X, Y, Z in file a.qcow2) by the select statements > or try to cache the entire qcow2 file? > > 3) IO-Cache only helps with speeding up reads, right? In my mind, the > world is very bursty. It would be incredibly cool if we had the > ability to write to the SSD drive during bursts to return success to > the client quickly and then stream those writes at steady speed to the > SATA array. I realize this is more complicated then it sounds in > practice because incoming reads expect coherent data even while the > data is being slowly written to SATA but just curious if this is out > there. > > Thanks!
