On 11/08/2014 07:35 PM, Dmitri Maziuk wrote:
> On 11/8/2014 5:36 AM, Kern Sibbald wrote:
>
>> I think so. If I understand correctly, you want disk mount points or
>> directories to be treated much like a tape drive, so that you can
>> mount multiple "disks".
>>
>> I think this feature is already implemented, with one difference ...
>> that when the device is mounted, it assumes that it has a
>> filesystem on it rather than treating it as a raw device.
>
> Either way works, filesystem makes it easy to see what's on it, but
> you have to mkfs on a new disk.
>
>> Much like the Virtual Autochanger feature, I am not 100% sure where this
>> is documented, so you may have to search for it. The main requirement
>> for it to work is to configure the SD Device (even if it is a disk
>> device) as removable.
>
> "Devices that require a mount (USB)" in
> http://www.bacula.org/7.0.x-manuals/en/main/Storage_Daemon_Configuratio.html#SECTION001730000000000000000
> says, among other things, "write part command must be defined". "Write
> part command" is somewhat documented in "Devices that require a mount
> (DVD)" in docs for 5.0 and below, but not in 7.0. Its purpose is
> unclear, my guess would be it's intended for "write to optical disk
> but not close it", no idea how or why that would apply to a usb stick.
It looks like the document is out of date. I am not sure we ever made a
pass through the manual to remove the DVD documentation. In any case, a
mount command may or may not be necessary for doing USB, but the "Write
Part Command" is definitely not needed and indeed not used any more.
>
> From reading that section I can't figure out the config for 12-bay
> hot-swap sata storage server where I can write to all disks and
> replace them as they get full, just like they were tapes. (But see my
> reading comprehension note below.)
I don't remember what the configuration would be, because I have not
used the feature for about 5 years, but the first step would be to play
with setting "Removable Media" to true, then looking at whether or not
"Requires Mount" and the "Mount Point" and "Mount Command" are needed.
If you have setup your USB to be automatically mounted, which seems to
be the default now, but was not when I used the feature, you may not
need any mount commands, though if the operator must explicitly remove
and replace a disk, I imagine they will be required.
>
>> By the way, in case you have not noticed, there are three white
>> papers posted on the bacula.org web site, two of them, if I am not
>> mistaken, document Virtual Autochangers as implemented in the
>> community version (slightly different from the Enterprise version).
>
> I notice now, thanks.
>
> CommunityDiskBackup.pdf has the same old problem in 2.1 Grouping
> Storage Devices: as usual, it talks multiple devices and shows 2
> Device definitions with Archive Device = /disk in both. Personally I
> don't know how to mount multiple physical devices in the same /disk at
> the same time and keep them separate too.
Bacula can only mount one device in any given Device section at a time,
but in an Autochanger (virtual or not) there are multiple Devices and
each can have its own directory. However, if you use different
directories, you must use different Media Types otherwise, Bacula will
not know the right directory to look in for "fixed" disks.
>
> Same goes for 2.2 Virtual Autochanger: it doesn't let you write to
> multiple (disk) devices, it lets bacula treat a single Archive Device
> as "multipe devices" -- presumably for concurrent access.
I am not sure why you believe the above. Each Device can have a
different Archive Device path. The examples probably use the same
directory so that it does not get too complicated (with Media Types and
all). I suggest you just try using different disk devices and see what
happens.
>
> Same goes for section 3 (Multiple Devices) in
> CommunityDiskBackupDesign.pdf
>
> At least that's what I read in there. Maybe I'm not reading it right:
> the years have not been kind and my leet reading comprehension skillz
> ain't what they used to be.
I think it is just that the examples are simpler than what you want to do.
>
> The rest of it is very useful but not germane to the topic of using
> multiple hot-swappable disks for storage.
In principle hot-swappable disks should work, but since I don't think
anyone has done it before, there may be hidden problems that I am not
aware of.
>
> This is all great but so far the only known config I've actually seen
> working is a vchanger. I'd consider buying it off and rolling it into
> bacula proper so instead of much handwaving and allegations of "maybe
> documented somewhere" features you'd have a definitive and working
> answer for retentive assholes like me.
I would say that if you are already using vchanger and it works for you,
you should stick with it. If someone is setting up a new configuration,
the Virtual Autochanger feature may or may not be able to solve their needs.
Best regards,
Kern
>
> Dima
>
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