HAMMER, disk mirroring and secure NFS

[Tomohiro Kusumi]

You can either directly copy between fses, or you can dump the binary
from one fs to stdout (and redirect it to a file) and later restore.
Both are technically the same thing.

The source fs can be either independent fs or some master PFS within
the fs. This comes from the fact that PFS is technically nothing much
different from the default fs itself. The default fs is actually just
another PFS whose id is 0. The idea of PFS is quite difficult to
understand and there's no good written document either.

In either of above cases, you need the both source and destination to
be already mounted as fs, otherwise you can't copy. It's HAMMER's
internal id number based logical copying, but not
device/partition/dataset/etc based copying.

> Can the mirror copy be accessed/mounted as a separate filesystem and if so, can every file be read file-by-file or can it only be restored as the whole dataset ???

There's no equivalent of ZFS's dataset. The whole idea is quite
different from ZFS even if it has some similarity in its feature.


2017-03-26 14:52 GMT+03:00 Jasse Jansson <jasse at yberwaffe.com>:
>
>
> On 2017-03-26 12:14, Michael Neumann wrote:
>>
>>
>>> 1) On my main PC I'm planning to install DragonFlyBSD on a small SSD and
>>> use two 6TB disks for my home directory: one disk for the master PFS,
>>> one as a copy with HAMMER's mirror feature.
>>> I have a 7200 rpm Seagate IronWolf and a 5400 rpm Western Digital Red.
>>> Can I use them together or HAMMER's mirror feature requires (or work
>>> best with) identical disks (or disks from different brands but same
>>> speed)? If I can use them do you suggest using the faster disk for the
>>> master or the mirror?
>>
>> No problem here. You can even mirror over slow internet connections.
>> HAMMER is using logical mirroring, i.e. it creates two completely
>> separate file systems (with identical logical content), so neither the
>> physical block size, nor the speed of the disk matters. Of course you
>> have to give the second slower disk enough time to keep track.
>
>
> A related question:
>
> Can the mirror copy be accessed/mounted as a separate filesystem and if so,
> can every file be read file-by-file or can it only be restored as the whole
> dataset ???
>
> I belive that ZFS mirror-stream (or what it's called) can only be restored
> as the whole shebang but I have never tried it myself.
>
> Long time since I had DF installed on a computer, might mitigate this today
> but I don't have enough HD's to try this mirroring thing by myself right
> now.
>