[DRBD-user] newbie Q: 'two drbd devices on the same spindle' and spindle is raid box

Todd Denniston Todd.Denniston at ssa.crane.navy.mil
Thu Jan 22 16:23:43 CET 2004

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


Hi,
[drbd-0.6.10, Fedora Core release 1, 2 node]
As I was beginning to create my drbd.conf, using the
/usr/share/doc/drbd-0.6.10/drbd.conf example, I read the following comment:

        # btw, don't do this.
        # did you notice that in this example we have two drbd devices
        # on the same spindle (hda)?  performance will be bad.  if you
        # use several drbd devices, put them on different spindles;
        # different channels/controllers won't be a bad idea for IDE.

I have a raid box [Promise RM8K, RAID 5, ~750GB, SCSI], which presents itself
as one disk, AKA spindle, and I wanted to know if the above note was mainly
for [IDE|single physical spindle] or if it also badly affects RAID boxes
presenting as one disk?

Is this because DRBD/EXT3 makes some assumptions about stacking up writes that
are not true when presented with multiple partitions, or just that the seek
times get amplified badly with drbd in protocol=C?

I wanted to split the space up into partitions such that business functions
[cvs & project storage] would be less troubled by disk hogs home directories.

can or is it wise, to have drbd mirror the whole device sda and have
partitions in it?

-- 
Todd Denniston
Crane Division, Naval Surface Warfare Center (NSWC Crane) 
Harnessing the Power of Technology for the Warfighter



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