Host-based backup of Microsoft Hyper-V VMs.
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matteu
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iSCSI Repository RDM or within guest OS

Post by matteu »

Hello,

I would like to know if there is some difference to connect repository with iSCSI between :

-Use hv host initiator to connect to storage and then add lun as RDM disk to repository VM
-Use in guest initiator iSCSI and use 2 network adapter (one for the vm itself and the other for the storage)

I don't find anything about it on the Veeam best practice guide on the storage section.

Thanks for your help :)
soncscy
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Re: iSCSI Repository RDM or within guest OS

Post by soncscy »

I don't think there's a practical answer from the software side here as it's all about where you want to focus your management efforts.

RDM is useful because you configure once at the host level and get all the benefits and don't have to deal with the network abstractions that might kill off some features you rely on.

iSCSI is "simpler" to set up initially

Performance wise I think at this stage in HyperV and VMware you should get pretty good performance on both sides, but some things to consider (in no particular order):

- Performance is about equal
- Not sure if this is true anymore, but I think live migration becomes a concern with RDM if the other hosts don't also have access configured to the storage but worth investigating since you don't want your repository bound to a single host
- iscsi can be detached and reattached to new machines pretty fast, RDM will take some configuration time
- you need to check the network at two layers with iscsi; the virtual networks and the physical (i.e., MPIO is useless if you set it up in guest but only have a single NIC over which the traffic might leave the HyperV environment)
- A lot easier to reboot a virtual machine than a host for patching issues to correct iscsi bugs (MS has tons of them over the years)

Ultimately, "pick your poison" :) You'll have some management considerations with both approaches, and it's just whichever you feel more comfortable with.
matteu
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Re: iSCSI Repository RDM or within guest OS

Post by matteu »

Thank you for your answer.
Both are possible ok :)
Regnor
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Re: iSCSI Repository RDM or within guest OS

Post by Regnor »

I think the biggest advantage of in-guest iSCSI is that you don't use the virtualization layer. This removes a possible error source and lowers complexity; especially in case of a DR. Also it increases security a bit as a virtualization administrator can't easily manipulate the in-guest storage.
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