[Drbd-dev] roadmap draft
philipp.reisner at linbit.com
Tue Sep 7 15:49:15 CEST 2004
: Dipl-Ing Philipp Reisner Tel +43-1-8178292-50 :
: LINBIT Information Technologies GmbH Fax +43-1-8178292-82 :
: Schönbrunnerstr 244, 1120 Vienna, Austria http://www.linbit.com :
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DRBD 0.8 Roadmap
1 Drop support for linux-2.4.x.
Do all size calculations on the base of sectors (512 Byte) as it
is common in Linux-2.6.x.
(Currently they are done on a 1k base, for 2.4.x compatibility)
2 Drop the Drbd_Parameter_Packet.
Replace the Drbd_Parameter_Packet by a more general and
3 Changes of state and cstate synchronized by mutex and only done by
the worker thread.
4 Two new config options, to allow more fine grained definition of
DRDBs behaviour after a split-brain situation:
disconnect No automatic resynchronisation gets performed. One
node should drop its net-conf (preferable the
node that would become sync-target)
asf-older Auto sync from is the oder primary (curr.behaviour i.t.s.)
asf-younger Auto sync from is the younger primary
asf-furthest Auto sync from is the node that did more modifications
asf-NODENAME Auto sync from is the named node
disconnect (current behaviour)
asf-primary Auto sync from is the current primary
panic The current primary panics. The node with the
higher gc should take over.
1) The disconnect actions cause the sync-target or the secondary
node to go into StandAlone state.
2) If two nodes in primary state try to connect one of them goes
into StandAlone state (=curr. behaviour)
3) As soon as the decision is takes the sync-target adopts the
GC of the sync source.
[ The whole algorithm would also work if both would reset their
GCs to <0,0,0...> after the decision, but since we also
use the GC to tag the bitmap it is better the current way ]
5 It is possible that a secondary node crashes a primary by
returning invalid block_ids in ACK packets. [This might be
either caused by faulty hardware, or by a hostile modification
of DRBD on the secondary node]
Extend the block_id field. (currently 64 bit) by at least
32 bits (64?) . (=block_id_chk field). The primary node
stores an encrypted (random key, changes every 15 minutes...)
checksum (=signature) in the second field.
The secondary node can not fake (either intentionally or
unintentionally) these signature.
The primary node will only dereference the block_id pointers
if the signature is right.
6 Support IO fencing; introduce the "Dead" peer state (o_state)
drbdadm peer-dead r0
drbdadm [ considered-dead | die | fence | outdate ] r0
( What do you like best ? Suggestions ? )
remove option value: on-disconnect=freeze_io
New meta-data flag: "Outdated"
Let us assume that we have two boxes (N1 and N2) and that these
two boxes are connected by two networks (net and cnet [ clinets'-net ]).
Net is used by DRBD, while heartbeat uses both, net and cnet
I know that you are talking about fencing by STONITH, but DRBD is
not limited to that. Here comes my understanding of how fencing
(other than STONITH) should work with DRBD-0.8 :
N1 net N2
P/S --- S/P everything up and running.
P/? - - S/? network breaks ; N1 freezes IO
P/? - - S/? N1 fences N2:
In the STONITH case: turn off N2.
In the "smart" case:
N1 asks N2 to fence itself from the storage via cnet.
HB calls "drbdadm fence r0" on N2.
N2 replies to N1 that fencing is done via cnet.
N1 calls "drbdadm peer-dead r0".
P/D - - S/? N1 thaws IO
N2 got the the "Outdated" flag set in its meta-data, by the "fence"
command. I am not sure if it should be called "fence", other ideas:
"considered-dead","die","fence","outdate". What do you think ?
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