ZFS tuning/usage on Qubes OS

[Euwiiwueir]

Hi fellow ZFS enthusiast,

@disclose-mushy

• Do you use dedup for your VMs?

No. Have wanted to try this, but haven’t done the experiment:

@Euwiiwueir

I am curious if it could have useful application specifically for a TemplateVM dataset in the zpool, for users who have many custom templates. I have very many templates, most of which are dupes of each other modulo a few packages. If all of these templates, and only templates, and perhaps only the root images of the templates, were placed in a dataset with deduplication enabled and a large recordsize (1 MB or greater) then perhaps the costs would be workable.

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• What recordsize do you use?

See:

@likeafox

recordsize isn’t applicable to qubes, because qubes use zfs volumes not filesystems. recordsize is for filesystems. I think the analog for volumes would be volblocksize.

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• What compression algo do you use?

I have been using the default lz4, but @likeafox makes a compelling point IMO:

@likeafox

I won’t say it could never be an acceptable risk, however I’m never going to recommend anyone use compression on a Qubes pool, because it breaks isolation between dom0 and your qubes. By using compression you are tasking dom0 with running compression/decompression algorithms on data that is provided by guests. Those are algorithms which are not immune to security vulnerabilities. In fact I would recommend anyone currently using it to disable compression at least until they’ve seriously considered the risk.

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• Which Qubes pool driver do you use, ZFS or file-reflink?

ZFS

• How do you organize your datasets?

Currently, one dataset for dom0 root, one for dom0 swap (possibly risky but has never been an issue), and one dataset for a single vm-pool. I would like to try an additional dataset for template dedup (referred to above) but I have enough free space there hasn’t been a need for it beyond curiosity.

• How do you mitigate/handle zpool fragmentation?

Can you say more about what you’re observing?

• Do you use ZFS as your rootFS?

Yes; has been working fine, and it makes me feel good, but it’s a little dicey to set up.