Hi to all,
What if you're using an ISCSI gateway based on LIO and KRBD (that is, RBD block device mounted on the ISCSI gateway and published through LIO). The LIO target portal (virtual IP) would failover to another node. This would theoretically provide support for PGRs since LIO does support SPC-3. Granted it is not distributed and limited to 1 single node throughput, but this would achieve high availability required by some environment. On Wed, Oct 11, 2017 at 12:26 PM, David Disseldorp <ddiss@xxxxxxx> wrote:
Hi Jason,
Thanks for the detailed write-up...
On Wed, 11 Oct 2017 08:57:46 -0400, Jason Dillaman wrote:
> On Wed, Oct 11, 2017 at 6:38 AM, Jorge Pinilla López <jorpilo@xxxxxxxxx>
> wrote:
>
> > As far as I am able to understand there are 2 ways of setting iscsi for
> > ceph
> >
> > 1- using kernel (lrbd) only able on SUSE, CentOS, fedora...
> >
>
> The target_core_rbd approach is only utilized by SUSE (and its derivatives
> like PetaSAN) as far as I know. This was the initial approach for Red
> Hat-derived kernels as well until the upstream kernel maintainers indicated
> that they really do not want a specialized target backend for just krbd.
> The next attempt was to re-use the existing target_core_iblock to interface
> with krbd via the kernel's block layer, but that hit similar upstream walls
> trying to get support for SCSI command passthrough to the block layer.
>
>
> > 2- using userspace (tcmu , ceph-iscsi-conf, ceph-iscsi-cli)
> >
>
> The TCMU approach is what upstream and Red Hat-derived kernels will support
> going forward.
SUSE is also in the process of migrating to the upstream tcmu approach,
for the reasons that you gave in (1).
...
> The TCMU approach also does not currently support SCSI persistent
> reservation groups (needed for Windows clustering) because that support
> isn't available in the upstream kernel. The SUSE kernel has an approach
> that utilizes two round-trips to the OSDs for each IO to simulate PGR
> support. Earlier this summer I believe SUSE started to look into how to get
> generic PGR support merged into the upstream kernel using corosync/dlm to
> synchronize the states between multiple nodes in the target. I am not sure
> of the current state of that work, but it would benefit all LIO targets
> when complete.
Zhu Lingshan (cc'ed) worked on a prototype for tcmu PR support. IIUC,
whether DLM or the underlying Ceph cluster gets used for PR state
storage is still under consideration.
Cheers, David
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