On 1/31/2020 10:25 AM, dmaziuk via Bacula-users wrote:
On 1/31/2020 3:33 AM, Radosław Korzeniewski wrote:
Amanda had "RAIT" since forever.
If you would be so kind and have an idea how it could be implemented in
bacula and so kind to describe it on this list it would be
implemented by
developers.
I don't have any idea how it could be implemented *in bacula* since I
never looked at any bacula code.
In general sending the same stream of bytes to two different places
instead of one is not exactly rocket science. I guess it and can be
implemented in several places, e.g. special storage inside SD, or two
different SDs.
Actually, it is pretty tricky from user space and why the need for the
md kernel module in Linux. For true RAIT, like for RAID, it should be a
device driver. Most do not need RAIT, but I know some (Oak Ridge
National Lab, for one) use RAIT systems both for redundancy and
striping. Similarly, DRBD does this for block devices located on
separate machines, a network RAID-1, and again requires kernel-space
drivers. So implementing this in user space is still just making a copy,
because there would be no way to make a write atomic. And in that case,
what is wrong with using Copy jobs?
I would probably send to two SDs at once because it allows for more
flexible setups: the 2nd SD can write to "the cloud", it can be on the
off-site box, etc. Whereas amanda-style RAIT device only protects
against single disk/tape failure.
Dima
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