Xen devel - Sep 2007 - LVM/DRBD8/Xen - issue(s) in block-IO implementation?

Hi,

while trying to use Xen, DRBD and LVM together I came across a nasty  
issue with the following error message "bio would need to, but  
cannot, be split". It happens if one starts a LVM-based DomU.

There have been some postings regarding the same issue on the xen- 
users-list, but none of the developers ever commented on those.

So I would like to draw some attention to this issue on the developer  
list ;-).

It''s perfectly described in the following posting:

http://lists.xensource.com/archives/html/xen-users/2007-08/msg00338.html

I can add, that Xen and DRBD and LVM did run without such problems  
while using Xen 3.0.3 (Debian) and DRBD8, but started showing the  
issue with Xen 3.1.

The message just appears if one uses LVM volumes on DRBD devices as  
"phy:"-disks; if you mark such devices with "tap:" it works.

The DRBD developers point to Xen for fixing the issue. There are two  
threads which may lead in the right direction for someone familiar  
with block-IO in Xen:

http://lists.linbit.com/pipermail/drbd-user/2007-April/006728.html

http://lists.linbit.com/pipermail/drbd-user/2007-August/007269.html

http://lists.linbit.com/pipermail/drbd-user/2007-August/007270.html  
(just a followup to the former)

Thanks in advance for looking into it.
Peter


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On 7/9/07 11:41, "Peter Siering" <lists@siering.org> wrote:
> The message just appears if one uses LVM volumes on DRBD devices as
> "phy:"-disks; if you mark such devices with "tap:" it
works.
> 
> The DRBD developers point to Xen for fixing the issue. There are two
> threads which may lead in the right direction for someone familiar
> with block-IO in Xen:
Our bio-creation loop in blkback.c is very similar to that described in the
last email you reference. We certainly use bio_add_page(). Unfortunately
DRBD+LVM is not a test configuration that we have tested ourselves.

 -- Keir



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