Re:HGST gets closer to shipping 10TB HDD
by gamegoblin on Friday March 13, 2015 @01:30AM
(#9195784)
You only need to rewrite the whole zone if you want to modify something that's before the write pointer. That is, you can write data sequentially without penalty. It's modifying existing data that's the issue.
> You would need some sort of battery backed scratch/cache area to pull this off
Or a copy-on-write filesystem. With some tweaking they can essentially fill one zone by linearly writing new copies (and metadata) to it while garbage-collecting (copying GC, with compactation) old zones in the background
Having maybe 16 to 64 GB of flash storage (for writeback cache) would probably make a significant difference here. I think over the next five to ten years tiered storage will probably go mainstream.
Tiered storage is already here. If you're using block storage in the cloud those guys are already do all sorts of optimizations (for their costs) that include tiering. And on your own desktop / own server side you can do this today on Linux with bcache or dm-cache. Works great for databases.
You have to write 256MB to change a single bit?
And you have various zones, and you have to keep track of where data is written, because it's not written in order, and can be on any zone?
You would need some sort of battery backed scratch/cache area to pull this off, so that you don't have to write very often, otherwise I can't imagine performance will be very good.