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Re: [Xen-API] XCP and cloud storage advise needed

> Wouldnât a SAS HBA be similar to an FC or hardware iSCSI HBA? 


Yes. I do recall someone once using shared-SAS HBAs with the LVMoHBA SR (this is distinct from LVMoISCSI but shares common code) â itâs just a different wire transport. There might be checks in the LVMoHBA Python to only use fiber channel HBAs but that could probably be fairly easily circumvented. As long as your array allows multi-writer shared access to LUNs over SAS then XCPâs shared LVM mode (as described by George) should work fine.




From: xen-api-bounces@xxxxxxxxxxxxx [mailto:xen-api-bounces@xxxxxxxxxxxxx] On Behalf Of George Shuklin
Sent: 29 September 2012 00:39
To: Clayton Weise
Cc: 'xen-api@xxxxxxxxxxxxx'
Subject: Re: [Xen-API] XCP and cloud storage advise needed


Well, AFAIK xcp use iscsiadm (open-iscsi) to initiate connection. How exactly iscsiadm initiate conenction in case of accelerated iscsi I don't know.

There is a huge stuff behind how XCP use LVM on iscsi.
1) XCP use LVM, not CLVM
2) XCP use own lock mechanism to save LVM from corruption. F.e. master in XCP 1.1 poll every host in pool before removing LV from VG to be sure it not used. And master force slaves to reread LVM metadata from PV (on iscsi) to get new table. Honesty I think this is not really very error prone and I do have experience of LVM metadata corruption during fail recovery. Not very pleasant experience.
3) XCP 1.1 (and 0.5, and probably 1.5) use patched version of LVM to support --master option. That patch is unavailable in xcp-xapi (debian/ubuntu version) because maintainers of LVM in debian will never accepts patches to LVM of that scale and invasiveness.
4) Theoretically you can try to change LVMoISCSI target to switch from iscsi to normal HBA usage, but that require some serious digging in python code (and may be some ocaml reading).

On 29.09.2012 03:16, Clayton Weise wrote:

Wouldnât a SAS HBA be similar to an FC or hardware iSCSI HBA?  How does XCP deal with a hardware iSCSI or FC HBAs and LUNs?  XCP just uses CLVM, which in theory should be able to share any centralized block device, right?  Or am I totally off base hereâ


From: xen-api-bounces@xxxxxxxxxxxxx [mailto:xen-api-bounces@xxxxxxxxxxxxx] On Behalf Of George Shuklin
Sent: Friday, September 28, 2012 2:42 PM
To: xen-api@xxxxxxxxxxxxx
Subject: Re: [Xen-API] XCP and cloud storage advise needed


AFAIK XCP does not supports shared SCSI SR. You can try adopt SR, but this is not simple task and require deep understanding of some XCP internals.

XCP can allow you to create few SR's for few hosts, but VMs on that host will be unmigrable (half of cloud gone). If you want to use XCP in full scale you need network attachable storage, NFS or ISCSI. (note: xcp-xapi in debian supports only NFS).

On 29.09.2012 01:11, Alexander Ivanov wrote:



I have rather general question about XCP - Cloud approach, not sure if it's appropriate here but would really appreciate any info.


I'm very new to XCP and the whole Cloud approach, though I've been using Xen 3.4 on CentOS 5 and KVM on CentOS 6 for quite a while. Our company has couple of racks with mostly Dell servers using local drives as VM images, plus few of the servers directly attached to Dell MD3200 (this is basically external RAID storage that can be shared by few servers with HBA cards - up to 8 ports per MD3200 connected to servers by SAS cables - cheap alternatives to 10G iSCSI infrastructure).


So, now I'm thinking about moving to Cloud infrastructure and my question is if there is any way to make this MD3200 (or MD1220 or whatever other external storage it can be using SAS - HBA instead of real iSCSI) available as a SR (storage resource) for my cloud? From what I see so far (I have installed XCP 1.4.90 with CloudStack 3.0.2) looks like the only way to make some resource available to several servers in the cloud is to use iSCSI (or NFS - basically network sharing). But I really hate to spend few grands on 10G NICs and 10G switch (they're still not cheap). If I just stick to Xen (or KVM) without the 'cloud' I can 'share' this external storage connected by SAS cables among 8 servers (which is all my 'cloud') fine. Perhaps I just missing something?


I would also appreciate any info from the actual users of XCP/KVM - what would you recommend as a 'cloud orchestration' software? Looks like CloudStack is best choice now (compared to OpenStack and OpenNebula)? I just want to make sure the solution I choose will be relevant in few years from now. 


Thank you

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