The common thread is I/O to a MegaRAID raid5 device.  Which is cause for
concern since the primary function of both machines where I've encountered
this problem is file-serving.

Perhaps I am just unlucky and have 2 bad MegaRAID cards in a row.  I'm trying
to understand this better, figure out if I am doing something wrong.

My procedure is create a RAID 5 volume on the megaraid, do a slow init. Reboot
the system into Linux, write a single large partition with parted, then put
one or more logical volumes on the drive.

The "hung" problem has cropped up under the following situations:

(1) pvcreate on the disk

(2) mkfs.ext4 on the volumes created on the disk

(3) writes to the filesystem on the disk

It's happened on 2 fileservers each with a megaraid.




On 11/14/2012 10:19 AM, Jamie Duncan wrote:
> is there a specific bug/bugs you're referring to?
>
> a hung task means that a process is sitting on a core waiting on a specific bit of I/O for > 120 seconds. Not the length of the entire process, mind you, which depends on countless inputs and outputs to complete, but something on the other side isn't answering for a very long time.  It usually means an unhealthy system at some level.
>
>
> On Wed, Nov 14, 2012 at 11:04 AM, Ken Teh <[log in to unmask] <mailto:[log in to unmask]>> wrote:
>
>     I've recently been encountering this problem trying to stand up a large RAID 5 disk server.  My first encounter was when I was doing write speed tests.  I thought I had solved this problem by letting the megaraid card complete a slow init of the volume before trying to create a linux filesystem on it and re-doing my speed measurements.
>
>     But I have just now encountered it again on a new RAID 5 volume which I also let complete a slow init over the weekend.  I was in fact trying to do a pvcreate on the volume when it hung.
>
>     Can anyone shed some light?  I see posts for it but everything I read suggests it's been taken care of.
>
>
>
>
> --
> Thanks,
>
> Jamie Duncan
> 804.571.0458