[DRBD-user] DRBD Performance in disconnected mode ?

Robert reg at elconas.de
Fri Oct 10 19:07:53 CEST 2008

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

Hello list,

I'm evaluating DRBD performance in various scenarios right now - values 
as expected except for one value.

    100% random write (8k)

When doing 100% wandom write of 8k with i/o meter I get (repeatable):

218 TPS for the lower level LVM volume (/dev/vg_something/drbd0)
111 TPS with a DRBD device in connected mode (Protocol A over cross over 
99 TPS with the same DRBD device beeing disconnected (StandAlone 
Primary/unknown - manually disconnected the device with "drbdadm 
disconnect all")

The Filesystem is XFS
The Hardware is BBU supported 3Ware with 2x SATA HDD's and write cache 
Config includes:
    al-extents       1021;

I wonder:

- Why is DRBD in connetced mode faster than in disconnected mode ?
- Why is the lower level LVM device so much faster (mount options are 
the same) ?

Any hints ?


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