On 12/10/17 05:10, Gandalf Corvotempesta wrote:
Previously i've asked about DRBDv9+ZFS.
Let's assume a more "standard" setup with DRBDv8 + mdadm.
What I would like to archieve is a simple redundant SAN. (anything
preconfigured for this ?)
Which is best, raid1+drbd+lvm or drbd+raid1+lvm?
Any advantage by creating multiple drbd resources ? I think that a
single DRBD resource is better for administrative point of view.
A simple failover would be enough, I don't need master-master configuration.
In my case, the best option was raid + lvm + drbd
It allows me to use lvm tools to resize each exported resource as
required easily:
lvmextend...
drbdadm resize ...
However, the main reason was to improve drbd "performance" so that it
will use different counters for each resource instead of a single set of
counters for one massive resource.
BTW, how would you configure drbd + raid + lvm ?
If you do DRBD with a raw drive on each machine, then use raid1 on top
within each local machine, then your raw drbd drive dies, the second
raid member will not contain or participate with DRBD anymore, so the
whole node is failed. This only adds DR ability to recover the user
data. I would suggest this should not be a considered configuration at
all (unless I'm awake to early and am overlooking something).
Actually, assuming machine1 with disk1 + disk2, and machine2 with disk3
+ disk4, I guess you could setup drbd1 between disk1 + disk3, and a
drbd2 with disk2 + disk4, and then create raid on machine 1 with
drbd1+drbd2 and raid on machine2 with drbd1+drbd2 and then use the raid
device for lvm. You would need double the write bandwidth between the
two machines. When machine1 is primary, and a write for the LV, it will
be sent to raid which will send the write to drbd1 and also drbd2.
Locally, they are written to disk1 + disk2, but also those 2 x writes
will need to send over the network to machine2, so it can be written to
disk3 (drbd1) and disk4 (drbd2). Still not a sensible option IMHO.
The two valid options would be raid + drbd + lvm or raid + lvm + drbd
(or just lvm + drbd if you use lvm to handle the raid as well).
Regards,
Adam
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