On Thu, Oct 30, 2008 at 01:18:47PM -0400, Doug Ledford wrote:
4/ auto-assembly needs to do the right thing on a SAN where multiple
hosts can each see multiple arrays. Clearly only one host should
write to any one array at one time (until I get some
cluster-awareness going, which I had hoped to work on this year,
but it doesn't look like I will).
In this case, I don't think read-auto is enough. We either need
to not assemble arrays when aren't known to belong to us, or we
need to assemble them read-only and require and explicit
read-write setting.
So we need some way to know which devices could be visible to
other hosts.
I could have a global flag in mdadm.conf "Options SAN"
I could have a SAN-DEVICES to match "DEVICES", but as just about
everything is "/dev/sd*" these days, I don't know if that would
work.
Any suggestions concerning this would be welcome.
The scariest suggestion, but probably the most complete and automated,
would be to have mdadm do a search on any constituent devices to find
out what the eventual low level driver is. If it's a fiber channel
driver, or iSCSI, then don't auto assemble. If it's sata/e-sata, or
local SAS, then it's more likely auto assemble is fine. But, that level
of mucking around in /sys for each device would probably be quite ugly.
unfortunately this will not work out correctly
1) it is fairly possible for an host to boot from fiber-channel, and to
run md over it (it is a fairly common setup here).
2) scsi supports shared storage, and i believe SAS does too.
L.
--
Luca Berra -- bluca@xxxxxxxxxx
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