[SOLVED] Can't add LVM on top of iSCSI: device already used by volume group unknown

[daniel.b]

I'm attempting to configure a Synology UC3200 as an iSCSI target for my proxmox cluster. The Synology is a dual controller HA setup with an active/active setup. I have created 2 iSCSI targets and 2 LUNs on the Synology device and have permissions set to allow all.

I have successfully created the iSCSI storage on my proxmox cluster. Use LUNs directly is set to false. When I attempt to add an LVM on top of the iSCSI, I get the following error:

create storage failed: device '/dev/disk/by-id/scsi-3600140539353769d20d0d42fcdb7e2d7' is already used by volume group '[unknown]' (500)

The first time I attempted this, the error message was different, but I don't remember what it was. All subsequent attempts result in the above error.

I have removed the iSCSI storage and re-added it but get the same message. In an attempt to locate the unknown VG referenced in the error message, I have executed the following:

lvm vgdisplay
  WARNING: Not using device /dev/sdk for PV FqzgIg-nk3O-Jm0P-20N2-JOwQ-wJcq-aMjcwq.
  WARNING: Not using device /dev/sdl for PV FqzgIg-nk3O-Jm0P-20N2-JOwQ-wJcq-aMjcwq.
  WARNING: Not using device /dev/sdm for PV FqzgIg-nk3O-Jm0P-20N2-JOwQ-wJcq-aMjcwq.
  WARNING: Not using device /dev/sdn for PV FqzgIg-nk3O-Jm0P-20N2-JOwQ-wJcq-aMjcwq.
  WARNING: Not using device /dev/sdo for PV FqzgIg-nk3O-Jm0P-20N2-JOwQ-wJcq-aMjcwq.
  WARNING: PV FqzgIg-nk3O-Jm0P-20N2-JOwQ-wJcq-aMjcwq prefers device /dev/sdj because device was seen first.
  WARNING: PV FqzgIg-nk3O-Jm0P-20N2-JOwQ-wJcq-aMjcwq prefers device /dev/sdj because device was seen first.
  WARNING: PV FqzgIg-nk3O-Jm0P-20N2-JOwQ-wJcq-aMjcwq prefers device /dev/sdj because device was seen first.
  WARNING: PV FqzgIg-nk3O-Jm0P-20N2-JOwQ-wJcq-aMjcwq prefers device /dev/sdj because device was seen first.
  WARNING: PV FqzgIg-nk3O-Jm0P-20N2-JOwQ-wJcq-aMjcwq prefers device /dev/sdj because device was seen first.
  --- Volume group ---
  VG Name               pve
  System ID
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  9
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                2
  Open LV               2
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               <28.96 GiB
  PE Size               4.00 MiB
  Total PE              7413
  Alloc PE / Size       7413 / <28.96 GiB
  Free  PE / Size       0 / 0
  VG UUID               9FZyHK-s3O9-cO04-YdSN-PKzn-ZRY8-plNJt3

As shown, the vgdisplay command does not show any other volume groups referencing an iSCSI target, just the local storage on the node.

I've seen reference to filters in other posts. Here is the filter settings in my /etc/lvm/lvm.conf file:

devices {
         # added by pve-manager to avoid scanning ZFS zvols
         global_filter=["r|/dev/zd.*|"]
}

My first question - how can I locate and remove this volume group reference to the iSCSI device?

Second question - I do not have multipath enabled, event though I have 6 different paths to the iSCSI LUN, as indicated by the warning messages in the above command. Is this a problem? Do I need to enable multipath so I have better control over how the nodes are communicating with the iSCSI storage?

Thanks for your time.

 

[bbgeek17]

yes you need to configure multipath and most of your other issues will go away:
https://pve.proxmox.com/wiki/ISCSI_Multipath

---

Blockbridge : Ultra low latency all-NVME shared storage for Proxmox - https://www.blockbridge.com/proxmox

 

[daniel.b]

Thanks for your quick reply. Setting up multipath on all cluster nodes did the trick and I was immediately able to add an LVM on my iSCSI storage. Thanks for the tip!