Is it possible to configure software RAID 5 on linux that uses system RAM for write cache? I have a file server with 8GB of RAM ... would be really cool if I could dedicate 4GB to write cache. If so, how is this done? Thanks.
That's kinda awkward due to read-write cache is always there in despite of having RAID or a single disk block device. But there's one knob which can add more RAM for RAID's own stripe-cache: /sys/block/mdYOUR_MD_NUMBER/md/stripe_cache_size
This knob is addressed to lower "partial write" performance issue, AFAIS. It's meaning is number of cache pages (4k) per every disk drive in RAID.