0.7 performance, attack of the seek? [Was: Re: [DRBD-user] 0.6 vs. 0.7 3ware performance? [Was: Expectedsyncspeed for a 425gb volume?]]

Todd Denniston Todd.Denniston at ssa.crane.navy.mil
Fri Apr 8 00:58:09 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.

Todd Denniston wrote:
> Nate Carlson wrote:
> >
> > Just leave 128mb available on each disk?
> >
> _in_ each _partition_ used by drbd, or _as_ a separate _partition_ for each
> drbd partition.
> I plan that when I update ours, I will add a separate hard disk to the
> system which will be just used for drbd metadata partitions, so I don't have
> to worry about did I tell 0.6 config the correct amount smaller, or remember
> to up the size in the drbd config when I go to 0.7.

In the systems that have been having trouble getting the speed they want out
of 0.7, has anyone tried putting the metadata on a separate physical disk
(not in the same RAID either)?

Although I have not read the code, I suspect that a write in 0.7 (as seen by
the lower level device with ext3 on top of drbd) might go something like:
seek & write to filesystem location
seek & write to filesystem journal location (this might happen first)
seek & write to drbd metadata location

and I expect the metadata will require a big seek, even on a RAID. 

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

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