> I didn't realize that RAID cache doesn't help on reads (like RAM disks do).
Yeah, a lot of people have never really thought about it much. I've worked with database servers for years though, where we actually tuned that type of hardware. The main difference is that a write doesn't return a block to the application, so it can return immediately without physically writing to disk, just putting the blocks in the RAM cache until it has some spare iops to burn or the cache becomes full. For reads though, you have to block until you have physically pulled the block off the disk so that you have something to return. RAID controllers do support predictive read-ahead caching, but that only makes a difference if you have sequential access patterns e.g. streaming large files. Otherwise, it has to block until it pulls data off the spindle every time because it doesn't know what you'll ask for next (unless you get very lucky and the data is in cache). So it is primarily good for streaming large files (e.g. video editing) or buffering write bursts (e.g. database servers). > Just how expensive is a high-performance 50GB RAM disk system? Expect to pay ~$2 per MB on the cheap end of things. Or for 50GB, about $100k. Using cheap machines maxed with RAM and RDMA fabrics or similar is a cheaper way to do this for roughly equivalent performance, but you won't be able to do this on Windows -- this is one of those arenas where Linux excels. cheers, j. andrew rogers ------- To unsubscribe, change your address, or temporarily deactivate your subscription, please go to http://v2.listbox.com/member/[EMAIL PROTECTED]
