HAMMER, disk mirroring and secure NFS

[Jasse Jansson]

On 2017-03-26 14:41, Tomohiro Kusumi wrote:
> 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.
A PFS is more like a namespace, I got that.

> 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.
Poorly worded question, apperantly. I'll try again.

Can the target PFS (the mirror) be mounted (yeah, I know, read only) and 
then accessed as any other filesystem, i.e. I can ls, cd and then cp a 
single file from the ro-pfs-mirror to another filesystem ?

>> 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.
>>