It was wrong back then and it's wrong now
Posted Nov 6, 2008 16:20 UTC (Thu) by khim
In reply to: Wrong direction!
Parent article: Linux and object storage devices
For rotating storage it hides bad block remapping. For flash storage it hides wear levelling and delete-before-write.
Yes - and I've certainly had problems with the first and I'm sure I'll have problems with the second. The only sane way to resolve this problem is to offer as low access as possible - but not lower. I don't think checksum calculation for blocks on HDD belongs to OS kernel (it can be calculated in HDD more or less for free, but general-purpose CPU will spend significant power doing it), but bad blocks handling certainly should belong to kernel - it have more resources to cope.
The search isn't for the lowest possible abstraction to present to the computer, the search is for the abstraction which best mediates between the needs of the computer and the needs of the storage.
Puhlease. What have this search offered us now? Predictable and mostly unlreliable HDDs and SSDs? I'd prefer raw flash, thank you.
It's a lot simpler to build complex storage (with features like migration between flash, disk and tape) if the storage is told what blocks are in a file rather than being left to guess.
What is the goal: great storage subsystem or great system? If the latter then all these things must be done at the system level (and may be offered via NFS/CIFS).
Please note that I'm not a OBS defender, I'm only seeking to explain it. Conversely, I'm also not saying that OBS is such a poor idea that it shouldn't be in Linux.
OBS is quite bad idea but Linux will need some support for it anyway. And it's useful is some strange places (for example in KVM/VMWare/Xen).
to post comments)