[DRBD-user] Raid1/Drbd read performance

Sebastian Riemer sebastian.riemer at profitbricks.com
Mon Aug 26 09:44:30 CEST 2013

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

Hi Mario,

this is a design issue. Doing the replication on the target has its
disadvantages. If you want to have the read balancing feature, then you
would have to move the replication to the initiator (e.g. by using MD
RAID-1). You need symmetric (same) latency to both replica.

Actually, DRBD in Primary-Secondary with iSCSI has better read than
write performance - but only as writes are damn slow as you have chained
network paths instead of parallel ones.

Please have a look at the last slide of my presentation on LinuxTag this
year. There you can see the issue:


We've hacked MD RAID-1 for high-performance replication.


Sebastian Riemer
Senior Linux Kernel Developer - Storage
at ProfitBricks

On 25.08.2013 14:35, ml ml wrote:
> Hello list!
> I am using xen with drbd which is attached to two iscsi targets.
> On normal hardware raid controllers the read is done from two disks ( so
> u get about twice the read performance).
> Does Drbd support this? (reading from secondary over the network)
> Thanks,
> Mario

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