large filesystem & fileserver architecture issues.
hahn at physics.mcmaster.ca
Thu Aug 7 15:15:01 EDT 2003
> I read the abstract last evening and got a taste for it. That is really a
> remarkable idea to use the ethernet checksum for data integrity of stored
> data. Thanks for the heads-up.
for me, the crux of the idea is:
- if you want big storage, $/GB drives you to IDE.
- IDE is not amazingly fast, reliable or scalable.
- building storage bricks out of IDE makes a lot of sense,
since they can now be quite dense, low-overhead, etc.
- ethernet is a wonderfully hot-pluggable interconnect for this
kind of thing.
- doing raid over a multicast-capable network is pretty cool.
- using eth's checksumming is pretty cool.
- doing it this way (all open-source, including software raid)
means the system is much more transparent - you are not dependent
on some closed-source vendor tools to control/monitor/upgrade
Ben's approach (along with Lustre, for instance) seems very sweet for HPC
type storage needs.
one thing I do ponder, though, is whether it really makes sense to hide
raid so firmly under the block layer. it's conceptually tidy, to be sure,
and works well in practice. but suppose:
- to create a filesystem, you hand some arbitrary collection of
block-device extents to the mkfs tool. you also let it know
which extents happen to reside on the same disk, bus, host, UPS,
geographic location, etc.
- you can tell the FS that your default policy should be for
reliability - that raid5 across separate disks is OK, for instance.
or maybe you can tell it that a particular file should be raid10
instead. or that a file should be raid1 across each geographic site.
or that updates to a file should be logged. or that it should
transparently compress older files.
- the FS might do other HSM-like things, such as incorporating
knowlege of what's on your tape/DVD/cdrom's.
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