Hi Matthew, this is a very good question to start with. I am in fact very surprised by two things:
1. The results I have on a cached filesystem are not that far away from those I am getting from a not-cached FS; 2. The results I am getting as write performance seems very far from those that are exposed for a similar benchmark on bcache front page (accounting for tens of thousand IOPS). I understand that my benchmark is done on a cached partition set up as a LVM, and on a file laid out on a XFS formatted VG. This must have a cost, but this huge ? I also understand that the SSD on my laptop may have poorer performances than the one used by Kent for his benchmark, yet the difference is huge (18.5K >> 454). Hence my eyebrows rising... Cheers, Leslie. On Wed, May 1, 2013 at 5:36 PM, matthew patton <[email protected]> wrote: >> I am obtaining the following figures, on a cached fs: >> seq-read: iops=12188 >> rand-read: iops=7392 >> seq-write: iops=430 >> rand-write: iops=454 > > Just what numbers were you expecting to see? A decent 7200RPM drive can only > muster 70 IOPs on a good day. The lies the SSD vendors print in their > literature and on the side of the box are almost always done with a blocksize > of 512 bytes. So if you're doing 4K operations, divide by 8 at least. -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
