[p4] Trying to understand the benefits of "Warning! We stronglyrecommend that you set up your system so that the journal iswritten to a filesystem other than the P4ROOT filesystem."
sstevens at adobe.com
Fri Nov 17 13:42:54 PST 2006
Your analysis makes sense to me, I have never understood the importance
of having the journal on a separate volume. If the db files and file
archives are both gone, the journal file has only small usefulness
giving you a very cryptic presentation of what changed since the last
checkpoint. It is possible that you could lose just your db files
through a fat-fingering accident, but you'd probably still have your
local journal file.
This assumes that you always backup your archive files AFTER creating a
checkpoint, which is the way to do it. Since you have to fall back to
the last backup, you want only what is in that checkpoint, not what is
also in a journal file from after the checkpoint.
From: perforce-user-bounces at perforce.com
[mailto:perforce-user-bounces at perforce.com] On Behalf Of John D'Albis
Sent: Friday, November 17, 2006 1:06 PM
To: perforce-user at perforce.com
Subject: [p4] Trying to understand the benefits of "Warning! We
stronglyrecommend that you set up your system so that the journal
iswritten to a filesystem other than the P4ROOT filesystem."
Currently, we have the journal and depot files on the same physical
disk. We don't follow how this change would actually help in a
restore... It is repeated several times in the admin guide making it
appear to be an imperative:
The only use we can determine for having this file on a separate file
system is that, if we were to lose only the non-journal disk - it will
show which updates will not be included in the restore. What are we
missing? Here is our logic:
Assumptions: We do a checkpoint followed by a full backup every night
at 3 am. If, in the case of any disk failure, we want to be able to
restore to a known state as quickly as possible, with the least amount
of work lost. Journal and checkpoint are on disk A, *.db files and
Depot are on Disk B.
Scenario a) disk A crashes, lose Journal and checkpoint.
Recovery procedure: Install a new A disk - create new checkpoint file
and start a new journal. No work is lost.
Scenario b) disk B crashes, lose *.db and depot files.
Recovery procedure: Install a new B disk - restore depot from backup
AND recreate *.db files from checkpoint on Disk A. (While we also have
a journal file and hence the ability to restore the metadata to a state
that is newer than the depot, doing so would be fruitless as the depot
files themselves would only be at the state of our last backup - 3 am).
Work since 3 am is lost.
Scenario c) disk A & B crashes - lose everything!
Recovery procedure: Similar to scenario b. Work since 3 am is lost.
Is there a scenario that we're missing?
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