[Users] live migration (Re: SIMFS users)

[Kir Kolyshkin]

On 07/21/2015 06:41 PM, Gena Makhomed wrote:
>> For one thing, I wonder how you use live migration with zfs,
>> can you please tell us?
>
> I don't use live migration at all.
>
> several reasons:
>
> 1) currently even suspend/resume not work reliable:
> https://bugzilla.openvz.org/show_bug.cgi?id=2470
> - I can't suspend and resume containers without bugs.
> and as result - I also can't use it for live migration.

Valid point, we need to figure it out. What I don't understand
is how lots of users are enjoying live migration despite this bug.
Me, personally, I never came across this.

>
> 2) I see in google many bugreports about this feature:
> "openvz live migration kernel panic" - so I prefer make
> planned downtime of containers at the night instead
> of unexpected and very painful kernel panics and
> complete reboots in the middle of the working day.
> (with data lost, data corruption and other "amenities")

Unlike the previous item, which is valid, this is pure FUD.

>
> 3) my current hosting provider don't allow migrating
> of IP between different servers in his datacenter.
>
> 4) from technical point of view - it is possible
> to do live migration using ZFS, so "live migration"
> currently is only one advantage of ploop over ZFS

I wouldn't say so. If you have some real world comparison
of zfs vs ploop, feel free to share. Like density or performance
measurements, done in a controlled environment.

> - but this is not something like "killer feature",
> but only temporary situation. In near future this
> imbalance can be fixed, if anyone really need
> live migration and ZFS with OpenVZ.
> (using ZFS snapshots, for example)
>
> And, as result, in near future:
>
> "simfs over ZFS" always better (for app hosting)
> than "ext4 over ploop over ext4"
> - so it will be no reasons at all to use ploop.
>
> Also ploop is not in mainline kernel
> and probably newer it will be there. (?)
>
> Docker already contains ZFS storage driver.

I am working on a ploop graph driver for Docker.

>
> ZFS already can be used with mainline kernel.

But OpenVZ can't.

>
> With each new version - ZFS is better and better.

Do you imply that ploop is worse and worse with each new version?

> ZFS is really "The Last Word in File Systems",
> and now you can just use it for free,
> without reinventing the wheel.
>
> OpenVZ + ZFS or Virtuozzo + ZFS == atom bomb,
> killer feature with horrible devastation power.
>
> Or - you just forcing users to migrate from OpenVZ
> to CentOS+KVM over ZFS and/or CentOS+Docker over ZFS.
>