[DRBD-user] drbd 0.7.x newbe

Lars Ellenberg Lars.Ellenberg at linbit.com
Mon Apr 25 15:41:18 CEST 2005

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


/ 2005-04-22 14:12:58 +0200
\ Seuberth, Frank:
> Hello,
> 
> i am new to 0.7.x Version of drbd and have some questions.
> At first my configuration in the testing i am doing now:
> SLES9 and drbd 0.7.x (what ever i will have after online update).
> 
> 2 Systems, each configured :
> 3 Physical disks (hda/hdb/hdc 36GB each)
> hda1, swap, 1.5GB, software raid1 local to hdb1
> hda2, / ext3, 15GB, software raid1 local to hdb2

a note about (software) raid1 with IDE:
don't mirror the master to the slave on the same IDE channel.
always mirror between different channels, e.g. hda <-> hdc.

> hda4 ?? mtadata, upto 1GB raid 1 local to hdb4 ???

> hda3, /vol01 ext3, 18GB, drbddevice to node B /hda3
> hdb3, /vol02 ext3, 18GB, drbddevice to node B /hdb3
> hdc1, /vol03 ext3, 36GB, drbddevice to node B /hdc1
> 
> Here are my questions :
> I like to put the metadata on a physical partition.
> Is this partition yust a "raw device" with the parition
> type linux native or must there be a filesystem on it ?

no file system. the partition/block device is used as is.
(raw, if you want,
 though "raw devices" as a keyword is a different concept...)

> Should i put the metadata for all disks on the hda
> (hda4[0] for hda3, hda4[1] for hdb3, hda4[2] for hdc1)
> or each metadata on its own disk
> (hda4[0] for hda3, hdb4[0] for hdb3, hdc4[0] for hdc1)

if you think seektime for meta-data updates,
it is good to have meta-data on a different
physical device than the associated data storage.

but if one physical disk fails, you may lose the
storage of one and the meta-data of an other drbd.
oops.

in that situation, you have to NOT just drbdadm up
(or drbd start) the devices after you replaced the
physical disk. you should
# drbdadm attach all
# drbdadm invalidate "name of device which storage was lost"
# drbdadm connect all

you will see a full sync for the drbd of which the meta
data was lost (and got recreated), and a full sync for
the drbd of which only the storage was lost, but the
meta-data of which you just now invalidated.

if you put (only) the meta-data on a software raid,
you still need to invalidate it in case you lose the
physical storage device associated with it.

(btw, yet an other reason why I'd like to have a UUID
stored in the meta data block as well as in some block
on the physical storage device, when we have storage and
meta-data on different devices.)

	Lars



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