[DRBD-user] Large block IO bottleneck

Ross S. W. Walker rwalker at medallion.com
Tue Jan 2 22:05:24 CET 2007

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


Hi there I am using DRBD 0.7.21 with iSCSI Enterprise Target 0.4.14 on
CentOS 4.4.

When I run iSCSI direct to the LVM lv on top of hardware RAID I can get
225 MB/s over two sessions in MPIO with 256K block size, but when I put
DRBD in-between iSCSI and LVM the throughput tops out at 80 MB/s and I
can't seem to go over that.

DRBD seems to report it's max number of sectors as 8 (4K), does that
mean each io operation is limited to 4K? My hardware raid reports it's
max sectors as 128, could this explain the reduction to 1/3 throughput?



Ross S. W. Walker
Information Systems Manager
Medallion Financial, Corp.
437 Madison Avenue
38th Floor
New York, NY 10022
Tel: (212) 328-2165
Fax: (212) 328-2125
WWW: http://www.medallion.com <http://www.medallion.com> 



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