+++ This bug was initially created as a clone of Bug #147679 +++ The dm device using stripe target need to set readahead of the dm device properly (similarly to MD raid0 target). Also there is currently ignored --readahead parameter in lvcreate/lvchange. Computed or user defined readahead value should be propagated through libdevmapper library to dm device (using GETRA ioctl). Original bug report: Description of problem: LVM2 has a very bad reading performance using a larger disk stripe. Below is a single raw device out of a HP disk system (DS2405 to be exactly), connected via fibre channel (max 400 MB/s) to an HP DL145 (Opteron) machine: --- snipp --- [root@opteron ~]# time dd if=/dev/zero of=/dev/sdo bs=1024k count=10000 10000+0 records in 10000+0 records out real 2m36.544s user 0m0.017s sys 0m16.983s [root@opteron ~]# [root@opteron ~]# time dd if=/dev/sdo of=/dev/null bs=1024k count=10000 10000+0 records in 10000+0 records out real 2m20.435s user 0m0.023s sys 0m19.391s [root@opteron ~]# --- snapp --- This results to 64 MB/s writing and 71 MB/s reading; that's okay. Below is a disk stripe containing out of 14 HDDs with manual fibre channel multipath by LVM2 (at the same HP disk system): --- snipp --- [root@opteron ~]# time dd if=/dev/zero of=/dev/vg01/lv01 bs=1024k count=100000 100000+0 records in 100000+0 records out real 4m44.290s user 0m0.255s sys 3m28.193s [root@opteron ~]# [root@opteron ~]# time dd if=/dev/vg01/lv01 of=/dev/null bs=1024k count=100000 100000+0 records in 100000+0 records out real 9m32.262s user 0m0.276s sys 4m19.993s [root@opteron ~]# --- snapp --- This results to 350 MB/s writing and 175 MB/s reading - a worse result for reading. If I use a HP-UX box, I get ~ 350/350 MB/s; a good result. So the problem is LVM2. Version-Release number of selected component (if applicable): lvm2-2.00.31-1.0.RHEL4 How reproducible: Everytime, see above. Actual results: Only 50% reading performance compared with the measured writing speed. Expected results: Same reading speed like at writing or even better.
This request was evaluated by Red Hat Product Management for inclusion in a Red Hat Enterprise Linux maintenance release. Product Management has requested further review of this request by Red Hat Engineering, for potential inclusion in a Red Hat Enterprise Linux Update release for currently deployed products. This request is not yet committed for inclusion in an Update release.
fixed upstream
An advisory has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on therefore solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHBA-2008-0735.html