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In short: I´m building computer systems with mounted iSCSI storage. Is it possible to extend the iSCSI storage in live operating without rebooting the systems?

Details:

  • One LUN is planned with 5 TB of data.
  • For the beginning we want to start with 600 Gigabyte for the LUN.
  • The LUN is used for database systems.
  • We don't want to create a LUN with 5 TB. We want to keep them small, what gives us flexibility in moving storage.
  • We are using device-multipathing with two nodes.
  • I have created a lvm (with XFS) that gives the flexibility of merging the LUN´s and should allow for expansion in live operation.

About the last point I´m not sure and wanted to ask for other experiences in RHEL8 with GPDB and iSCSI.

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  • It is not clear who provide this LUN, RHEL? or some SAN storage? Draw the schema. Nov 15, 2022 at 11:45
  • The LUN will be provided by NetApp SAN. One problem is that the metro cluster is already on his edge. It will be extended in the future :)
    – STrike
    Nov 15, 2022 at 12:15

2 Answers 2

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Is it possible to extend the iSCSI storage in live operating without rebooting the systems?

Yes, very easily - simply extend the LUN at the Target end and run a scsi refresh. That should allow your client machine to see the extended LUN - if you've used LVM you can simply vgextend/lvextend and grow the filesystem.

That said what's wrong with simply using thin provisioning at the Target end and creating the LUN as 5TB one day-one - that way you won't ever need to extend it but also only store the data that's actually written?

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  • Thank you for the quick reply. I would use thin provisioning. One problem is that the Target (NetApp) is already relatively full. I want to create small LUN´s to provide flexibility in moving the LUN´s and concatenate them with LVM. Will my plan influence the IOps?
    – STrike
    Nov 15, 2022 at 12:21
  • Probably not no
    – Chopper3
    Nov 15, 2022 at 12:27
  • Before vgextend/lvextend you need to run lvextend to update LVM about the new size or this "disk" Nov 15, 2022 at 12:43
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You can provision on NetApp this LUN via thin provisioning to full size and it will extend as RHEL request more space in this LUN. So not need to play this game with extending.

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