ESXi host and NAS on single computer

[danswartz]

My drives were connected straight to the motherboard (using RDM) for the performance numbers I posted earlier in this thread, and I was definitely happy with those for these drives. However, I just couldn't write to the drives without errors/degrading pools (even a single-disk pool). Instead of troubleshooting that (there seems to be very little support for that method of RDM, and I don't see what I could have done wrong if the vmdk's created without errors),

I had 5 sata drives with RDMs passed in to zfsguru. Started running a benchmark and within minutes started seeing checksum errors and one drive dropping out for excessive errors. I assume something is buggy in the RDM stuff? Dropped that idea quick

 

[_Gea]

RDM would be a nice VMware feature.

But VMware does not support it - I suppose because of too much problems.
Use pci-passthrough instead (proper hardware support via vt-d or IOMMU needed)
-> less problems and better performance

Gea

 

[defuseme2k]

VMware DOES support RDMs on shared block storage, just not on local storage. ESXi free is limited to local storage only, so RDMs really aren't practical if that is the situation. There are a lot of newer people in here to virtualization in general, so be more specific. Maybe another vendor actually supports the passthrough on local disks, thats fine, but ESXi does not.

RDMs offer no real world performance gain, maybe 1-2% in some use cases, but that is ridiculous to use as a justification. This has been demonstrated many times, just do some google searching and figure things out for yourself (not directed at Gea, but anyone who reads this). All you're doing is adding complexity when there is NO justification for it. RDMs on local storage are not supported, and storage devices via VMDirectPath I/O are not supported either. Total lose/lose situation. I think it is ok to experiment and play around for the sake of learning, but if you're using it with data you'd like to actually keep, well, I'd suggest you color within the lines. Use VMDKs. VMware's virtual disk format is a proven technology, so if you're avoiding for the sake of not having your data encapsulated in that format, I'd say the apprehension is incorrectly placed.

RDMs can be justified, but only in use cases where it is actually required. For instance, it is required for setting up MSCS quorum. Performance is not a very good justification here.

 

[_Gea]

With vmdk on a storage os, you have two problems


1. extra layer with vdmk:
Solaris ZFS -> emulated ESXi disk driver -> ESXi vmdk -> ESXi disk driver -> disk
= lower performance, no ZFS failure management, more possible failure sources

instead of
Solaris ZFS -> Solaris driver -> disk
(via pass-through, a supported option with ESXi, only RDM to local disks is not supported)

2.
only with pass-through, you have native ZFS-disks, movable/ importable to another ZFS machine
(virtual or physical)


Gea