On Fri, 2007-08-03 at 14:41 -0700, Mark Carlson wrote:
> 7. root disk is seen through regular NIC port
There's a lot of detail left out here.
last I checked, solaris's iSCSI runs over the solaris IP stack, not over
a raw NIC.
A significant fraction of IP functionality (DHCP, IKE, routing, ipmp,
etc.,) involve significant amounts of user space code (commands and
daemons). Those daemons also make filesystem-related system calls and
do other things which may need disk i/o in normal operation.
If one of those daemons accesses part of the filesystem backed by an
iSCSI disk, I'd expect some sort of deadlock will be possible (syscall
made by routing daemon can't make forward progress without block X from
the root volume; iscsi can't fetch that block without being able to
transmit IP packets to the server; IP packets can't reach that server
until the daemon reestablishes a working route to the server; daemon
can't reestablish a working route until the aforementioned syscall can
make forward progress...).
I expect that running with an iSCSI root will have interactions with IP
which closely resemble operating with NFS diskless -- a capability that
is no longer actively used and which is not routinely tested.
while it may be possible to boot off an iSCSI disk, I suspect that there
are a bunch of dragons lurking here with respect to running reliably off
of iSCSI in non-trivial networks.
I'd feel a lot better about our ability to enumerate all these subtle
dependencies, gotchas, and limitations if this case got a full
(non-fasttrack) review.
- Bill
