[DRBD-user] One big drbd or several smaller ones ?

Lee Christie Lee at titaninternet.co.uk
Thu Jun 19 21:26:08 CEST 2008


OK it's a bit cheeky posting these kinds of questions to the list when
the guys at linbit offer consultancy, but since they haven't replied to
my contact and I'm an impatient man, here goes ;)

(PS linbit - I still want consultancy ;) get in touch when you can)


We are building two storage boxes - each of which has 2 x 73GB SAS 15K
spindles and 22 x 1TB SAS 7200 spindles (SATA disks with a SAS
interface).

The RAID cards we use are very good and we are intending to configure
the 22 spindles in a RAID-10 for optimum performance and redundancy.
(The other 2 disks a simple mirror)

The operating system and metadata will live on the mirror, the 11TB
array is to be used for data storage.

We plan on using around 8 separate filesystems, starting small and
growing over time as I don't think an 11TB filesystem is a good idea ;)

So - LVM is required.


Plan A
------
Take the 11TB array (/dev/sdb) and create a single partition on it.
Use drbd to replicate /dev/sdb1 onto the second node.
Create a single VolumeGroup from /dev/drbd0.
Create 8 LogicalVolumes from the VolumeGroup
Format each LogVol with reiserfs

Advantages :
+ single drbd resource (simple config)
+ single drbd metadata
+ no need to ever grow drbd resource;
  ..to grow, just increase LVM and grow fs.

Disadvantages :
+ eggs in one basket? Failure of drbd leaves us with no data, complete
restore required.
+ would growing LVM and fs be slow ?


Plan B
------
Take the 11TB array (/dev/sdb) and create a single partition on it.
Create a single VolumeGroup from /dev/sdb1.
Create 8 LogicalVolumes from the VolumeGroup
Use drbd to replicate each LogVol onto the second node.
Format each /dev/drbd[x] with reiserfs

Advantages :
+ if drbd were to corrupt or suffer issue, perhaps that issue would be
limited to one partition ?

Disadvantages :
+ Complex drbd configuration
+ 8 sets of metadata
+ Growth requires resize of LogVol, drbd and filesystem


If anyone has any views, I'm all ears :)

TIA.

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