Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On 2005-07-06T11:22:09, Sven Schuster <schuster.sven at gmx.de> wrote:
> 1. When the secondary node is down for some time, no mirrored
> hard disk is replaced, how will it be re-synced when it comes
> up again?? Will a complete resync take place, or just the
> changed parts of the block device? If just the changed parts
> are synced, how are those changed parts determined, and what
> is the order in which those parts are synced?? Would such a
> partial resync retain transactions as done by applications??
With 0.7 onwards, only the modified parts are synced, which are tracked
in a combination of an activity log and a bitmap structure.
During the resync, which basically works from the beginning of the disk
to the end, the secondary will be "inconsistent" for a short period of
time.
> 2. drbd is independent from the kind of block device which is
> underneath it, right?? So, as long as the kernel itself can
> use a block device, it can be used by drbd, regardless if it's
> an ide drive, scsi, raid, or maybe even a ramdisk :-)
Yes.
> 3. are there any pitfalls in using drbd on top of hardware raid?
No.
> 4. one of the questions that came to my boss' mind and which is
> (more or less) directed to linbit: is there any guarantee that
> drbd will still exist in, say, 5 to 10 years from now?? What I
> mean is, if we use it at work, we well use it for quite some
> time and have to make sure that it isn't gone in two years...
> (please bear with me, I've been using linux for about 10 years
> now, I'm an open source freak, but my boss is not...and I'd like
> my opinions to be backed up by someone more knowledgeable, at best
> by someone from linbit :-) )
Well, first, this is Open Source - so even if drbd was "dropped", if you
had enough incentive, you could revive it. Also, given that the data is
1:1 on the disk, with just some additional data for drbd housekeeping at
the end of the drive, you can easily get access to it.
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Second, you can purchase a drbd support & maintenance contract from
Linbit.
Third, if you ask such a question, I'm inclined to point out that the
SUSE Linux Enterprise Server 9 ships with drbd 0.7 and will be
maintained for a couple of more years (I think 5), and SLES10 will also
include drbd and will be maintained for a couple of years too. Then the
question becomes: How likely is it for Novell to disappear and not
fulfill the support committment? Maybe that makes your boss more happy.
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Sincerely,
Lars Marowsky-Brée <lmb at suse.de>
--
High Availability & Clustering
SUSE Labs, Research and Development
SUSE LINUX Products GmbH - A Novell Business -- Charles Darwin
"Ignorance more frequently begets confidence than does knowledge"