Questions on expanding an iSCSI LUN

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brian.sorrells
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Questions on expanding an iSCSI LUN

Post by brian.sorrells » Tue Oct 30, 2018 11:09 pm

I have a TS-EC879U in an office location that hosts virtual machines located on an iSCSI thin LUN. The LUN has hit its capacity a few months ago and I expanded the capacity to compensate. This was apparently a bad idea seeing as the machine became inaccessible for some days and failed its expansion. I'm not sure what I'm doing wrong and do not want to repeat the error. My question is this; What are the best practices on expanding the capacity of a block-based iSCSI thin LUN that hosts virtual machines (VMware). Attached and embedded is a picture containing what I would assume are the pertinent details about the setup.

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storageman
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Re: Questions on expanding an iSCSI LUN

Post by storageman » Tue Oct 30, 2018 11:34 pm

So what state is it in now?
Personally don't like thin LUNs.
The process for expansion is modify the LUN on the Qnap side, then in Disk Manager expand on the Windows side.
If a LUN becomes full it will not mount.

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Re: Questions on expanding an iSCSI LUN

Post by brian.sorrells » Wed Oct 31, 2018 12:05 am

The LUN is operating fine, the status is online. The modifications only happen on the QNAP side since VMWare just reads objects off the iSCSI target. There isn't a Windows machine that accesses the LUN. I originally expanded the LUN capacity on the QNAP side which caused the issue initially. Sorry I did not explain that well in the original post.

The only thing I didn't do was to detach the datastore from vCenter but that sounds pretty extreme. I'm sure it's something simple I'm missing.

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Re: Questions on expanding an iSCSI LUN

Post by storageman » Wed Oct 31, 2018 12:13 am


brian.sorrells
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Re: Questions on expanding an iSCSI LUN

Post by brian.sorrells » Wed Oct 31, 2018 12:31 am

If I'm understanding the articles correctly;

Link 1; This article pertains to reclamation of storage in regards to instant allocation. My issue is expansion of capacity into the pool.

Link 2; This tutorial in configuring new LUNs in a VMWare environment is useful but doesn't address the issue of the post in which there is an existing LUN that can't expand into the pool

The management network and datastore traffic are routed through different vmnics so "traffic" isn't a problem and the last time it was tried the VMs were off so oplocks weren't in play to gum up the works. While I agree that thick LUNs do have some advantages thin LUNs do as well, and regardless they were made before I inherited them so it's a moot point. The QNAP guys are saying that the servers themselves need to be turned off but that doesn't sound right at all. Seems like I could just turn off the nic temporarily on the QNAP to obtain the same result without shutting down servers that have other functions. What do you think?

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storageman
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Re: Questions on expanding an iSCSI LUN

Post by storageman » Wed Oct 31, 2018 1:01 am

Turning off the NIc will not guarantee IO is committed.
So rescan of datastore doesn't work?
https://kb.vmware.com/s/article/1017662

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Re: Questions on expanding an iSCSI LUN

Post by brian.sorrells » Wed Oct 31, 2018 3:57 am

I guess I could;

1. Shut down the VMs
2. Disable the iSCSI NIC on the QNAP
3. Restart the QNAP (clearing and IO)
4. Expand the LUN
5. Reverse the order and spool everything back up.

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Re: Questions on expanding an iSCSI LUN

Post by caing » Fri Dec 25, 2020 12:16 am

Did you ever resolve this question? I have a very similar issue.
Thin LUN connected via ISCSI to VMWARE Centerthat is used as storage for a VM. I am not out of space in the LUN but would like to allocate more space to ensure we don't run out of space going forward. There is plenty of space in the overall storage pool to expand the LUN.
Did you use the steps you suggested or did you have to take another course of action?

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