kernel-packages team mailing list archive

[beardtree <dan@xxxxxxxxxxxxx>]

It would be great if @lifeless could try attempting to contact dm-devel
again. This is a very important patch that would provide large benefit
across a variety of systems.

-- 
You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux in Ubuntu.
https://bugs.launchpad.net/bugs/361733

Title:
  dmraid(fakeRAID) raid1 driver doesn't loadbalance reads

Status in “linux” package in Ubuntu:
  Confirmed

Bug description:
  This is a kernel bug.  Actually, it's intended behavior, but it
  shouldn't be.

  In theory, fake RAID and software RAID should be the same thing.  The
  only practical difference is where they get their metadata from.  One
  from the system BIOS, the other from the disk.  However, it turns out
  that they take two completely different code paths.  The fakeraid
  (dmraid) driver reads only from the primary disk, while the software
  raid (mdraid) driver implements load balancing for RAID1.  Of course,
  this difference isn't well-documented, resulting in people sometimes
  choosing the wrong one.

  (1) There's no good reason why there should be two separate software RAID1 drivers.  They should be merged.
  (2) In the meanwhile, people should be splashed with loud warnings that if they choose fakeraid, they'll not get the improved read performance that they expect.

  Here's the LKML discussion where I asked about this:
  http://kerneltrap.org/index.php?q=mailarchive/linux-kernel/2008/7/7/2370344/thread

  As far as I know, they haven't addressed this problem since.  I'm
  reporting this here, because I see Ubuntu as the distro that seems to
  take responsibility for fixing a lot of the silliness that others
  won't.

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/361733/+subscriptions