[DRBD-user] Several questions

[Jeff Tucker]

Hi, guys. I had several questions about DRBD that should hopefully be easy 
to answer. For background, I'm bringing up a new system with a pair of 
identical servers. I intend to failover a RAID-0 array created from 12 SCSI 
drives. The drives are configured as one big array and the entire thing 
will be replicated. I'd prefer to use the 2.6 kernel and I'm currently 
testing using 0.7 development releases of DRBD.

- Since I'm failing over the entire /dev/md1 array, do I need to specify a 
disk-size in my drbd.conf? I intend to put the metadata on the array as 
well. The filesystem will be added after the DRBD device is up (in other 
words, mkreiserfs /dev/nb0). So, I think I want the reiserfs filesystem to 
take up most of the md1 device and the metadata to take up the rest. Does 
this happen automatically if I just say to put the metadata on that same 
device and don't specify a disk-size?

- I rebooted the primary to test a failover. The system failed over to the 
secondary just fine. When the primary came up and the units started to 
sync, I got a kernel panic due to a Reiserfs journal-601 error that said it 
was trying to write past the end of the device. I meant to save the actual 
numbers, but it wasn't even close. It said the size was something like 
400000 and it was trying to write to 1500000. Could that be caused by a 
lack of the disk-size? I was running the 20040528 snapshot at the time but 
have since updated to the recent release candidate 1. In my testing, the 
system usually fails over fine and rebuilds. It was just this one time I 
saw an error.

- The drives being failed over are a RAID-0 array. If a drive fails, I'll 
be replacing it. This means that a bunch of data out of the middle of the 
array goes away. When I bring that machine back online, I can't just write 
the data that the primary has received while it has been offline, I need to 
write all that data plus everything that was on the now-replaced drive. 
Will DRBD handle this automatically? Will I need to force a full resync 
somehow?

- Pretty much the same question, but involving the metadata. If I replace a 
drive that includes some or all of the DRBD metadata, will I still be able 
to bring up the device when the system is restarted? Will DRBD realize the 
metadata is missing or corrupted and rebuild it?

Thanks, guys, for the help.

Jeff

-- 
jeff at jltnet.com