Messages in this thread | | | Subject | Re: document ext3 requirements | From | "Martin K. Petersen" <> | Date | Sun, 04 Jan 2009 22:33:51 -0500 |
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>>>>> "Rob" == Rob Landley <rob@landley.net> writes:
Rob> I wonder if the flash filesystems could be told via mount options Rob> that they're to use a normal block device as if it was a flash with Rob> granularity X?
I posted some patches a few months ago that allowed us to do this. In particular they expose the underlying I/O topology to the filesystems. That includes minimum, preferred and maximum I/O size for both read and write as well as alignment. The patches also allow stacking so we get alignment right on say LVM on top of MD on top of a partitioned disk.
At Kernel Summit/Plumbers Linus absolutely hated this idea in the context of SSDs. And I don't necessarily disagree with his point that intel (claim to have) solved this problem.
However, there's still lots of crappy devices out there that we need to support. And we absolutely need this for RAID (both software and hardware) as well. I've been meaning to post a new round of these patches. I'll take a look at them again this week.
The intent was to use the alignment and block sizes to honor erase block boundaries when merging requests.
SCSI already has knobs that expose the appropriate sizes although not many vendors implement them yet. I've been talking to a few SSD vendors about exposing similar parameters with SATA. Most of them are willing and will happily share this information. Other vendors stop responding when you ask them too many questions.
-- Martin K. Petersen Oracle Linux Engineering
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