[DRBD-user] Metadata on software RAID1 load slowlyness problem

Daniel van Ham Colchete daniel.colchete at gmail.com
Fri Dec 8 16:58:33 CET 2006

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

Hi Yall,

I'm building my very first DRBD RAID. I've been sucessfull and
everything is working great.

My current config is:
sda 400GB + sdb 400GB = md Software RAID1
sdc 250GB

sda 250GB + sdb 250GB = md Software RAID1
sdc 400GB

My problem is, when the DRBD`s metadata is allocated to a md partition
(internal or /dev/md5[0]) the load time is greater than 4 minutes.
What I mean by load is "drbdadm up drbd0". I had to recompile drbdadm
changing it's timeout value from 120 to 600 seconds because of that,
otherwise my distro wouldn't init the both drbd devices.

Them, on the server that the metadata is being stored at the plain sdc
disk, the load time is less than 2 seconds. Important: I'm using
exactly the same hardware to each size, all the 400GB sized
harddrivers are exectly the same.

So, I tried changing both metadata storage place to plain sata drives
and everything loaded in less than 2 secs.

I also tried storing the metadata in internal and exlusive MD
partitions but the load time were the same: 4-5 minutes to the 340GB
partition and 2' 5'' to the 194GB partition.

Looking through DRBD's source I found that the delay is probably
happening that the _drbd_md_sync_page_io of the drbd_actlog.c file.
Probabily at the wait_for_completion(&event); line.

I'm using the kernel 2.6.18 with DRBD 0.7.22. My kernel has the
BIO_RW_SYNC defined.

Maybe that the problem is in kernel because DRBD just doesn't know
that /dev/md? is an Software RAID. But maybe, somebody that understand
of DRBD and the kernel`s BIO layer might have some ideia about how to
solve this issue.

Does any user/developer knows what can be done?

Taking the metadata out of the RAID1 is not an option because I would
lose all my data in case one harddrive fails.

Thanks in advance for any help.

Best regards,
Daniel Colchete

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