Re: [BackupPC-users] Backing up a BackupPC server
2009-06-04 00:22:17
Hi,
You all bastard !
Pieter
On Thu, Jun 4, 2009 at 8:52 AM, Pieter Wuille <sipa AT users.sourceforge DOT net> wrote:
On Wed, Jun 03, 2009 at 07:36:22PM -0400, Jeffrey J. Kosowsky wrote: > Holger Parplies wrote at about 23:45:35 +0200 on Wednesday, June 3, 2009:
> > Hi, > > > > Peter Walter wrote on 2009-06-03 16:15:37 -0400 [Re: [BackupPC-users] Backing up a BackupPC server]: > > > [...] > > > My understanding is that, if it were not for the
> > > hardlinks, that rsync transfers to another server would be more > > > feasible; > > > > right. > > > > > that processing the hardlinks requires significant cpu
> > > resources, memory resources, and that access times are very slow, > > > > Memory: yes. CPU: I don't think so. Access times very slow? Well, the inodes > > referenced from one directory are probably scattered all over the place, so
> > traversing the file tree (e.g. "find $TopDir -ls") is probably slower than > > in "normal" directories. Or do you mean swapping slows down memory accesses > > by several orders of magnitude?
> > > > > compared to processing ordinary files. Is my understanding correct? If > > > so, then what I would think of doing is (a) shutting down backuppc (b) > > > creating a "dump" file containing the hardlink metadata (c) backing up
> > > the pooled files and the dump file using rsync (d) restarting backuppc. > > > I really don't need a live, working copy of the backuppc file system - > > > just a way to recreate it from a backup if necessary, using an "undump"
> > > program that recreated the hardlinks from the dump file. Is this > > > approach feasible? > > > > Yes. I'm just not certain how you would test it. You can undoubtedly
> > restore your pool to a new location, but apart from browsing a few random > > files, how would you verify it? Maybe create a new "dump" and compare the > > two ... > >
> > Have you got the resources to try this? I believe I've got most of the code > > we'd need. I'd just need to take it apart ... > > > > Holger, one thing I don't understand is that if you create a dump
> table associating inodes with pool file hashes, aren't we back in the > same situation as using rsync -H? i.e., for large pool sizes, the > table ends up using up all memory and bleeding into swap which means
> that lookups start taking forever causing the system to > thrash. Specifically, I would assume that rsync -H basically is > constructing a similar table when it deals with hard links, though > perhaps there are some savings in this case since we know something
> about the structure of the BackupPC file data -- i.e., we know that > all the hard links have as one of their links a link to a pool file. > [...] > This would allow the entire above algorithm to be done in O(mlogm)
> time with the only memory intensive steps being those required to sort > the pool and pc tables. However, since sorting is a well studied > problem, we should be able to use memory efficient algorithms for
> that.
You didn't use the knowledge that the files in the pool have names that correspond (apart from a few hashchains) to the partial md5sums of the data in them, like BackupPC_tarPCcopy does. I've never used/tested this
tool, but if i understand it correctly, it builds a tar file that contains symbolic hardlinks to the pool directory, instead of the actual data. This combined with with a verbatim copy of the pool directory itself, should
suffice to copy the entire topdir in O(m+n) time and O(1) memory (since a lookup of what pool file a certain hardlinked file in a pc/ dir points to, can be done in O(1) time and space (except for a sporadic hash chain)).
In practice however, doing the copy on the blocklevel will be significantly faster still, because no continuous seeking is required.
> I would be curious to know how how in the real world the time (and > memory usage) compares to copy over a large (say multi Terabyte)
> BackupPC topdir varies for the following methods: > > 1. cp -ad > 2. rsync -H > 3. Copy using a single table of pool inode numbers > 4. Copy using a sorted table of pool inode numbers and pc hierarchy
> inode numbers Add: 5. copy the pooldir and use tarPCcopy for the rest 6. copy the blockdevice
-- Pieter
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OpenSolaris 2009.06 is a cutting edge operating system for enterprises
looking to deploy the next generation of Solaris that includes the latest
innovations from Sun and the OpenSource community. Download a copy and
enjoy capabilities such as Networking, Storage and Virtualization.
Go to: http://p.sf.net/sfu/opensolaris-get _______________________________________________
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- Re: [BackupPC-users] Backing up a BackupPC server, (continued)
- Re: [BackupPC-users] Backing up a BackupPC server, Les Mikesell
- Re: [BackupPC-users] Backing up a BackupPC server, Peter Walter
- Re: [BackupPC-users] Backing up a BackupPC server, Les Mikesell
- Re: [BackupPC-users] Backing up a BackupPC server, Holger Parplies
- Re: [BackupPC-users] Backing up a BackupPC server, Jeffrey J. Kosowsky
- Re: [BackupPC-users] Backing up a BackupPC server, Pieter Wuille
- Re: [BackupPC-users] Backing up a BackupPC server, Jeffrey J. Kosowsky
- Re: [BackupPC-users] Backing up a BackupPC server, Les Mikesell
- Re: [BackupPC-users] Backing up a BackupPC server, Jeffrey J. Kosowsky
- Re: [BackupPC-users] Backing up a BackupPC server, Les Mikesell
- Re: [BackupPC-users] Backing up a BackupPC server,
Lai Chen Kang <=
- Re: [BackupPC-users] Backing up a BackupPC server, Holger Parplies
- Re: [BackupPC-users] Backing up a BackupPC server, John Rouillard
- Re: [BackupPC-users] Backing up a BackupPC server, Pieter Wuille
- Re: [BackupPC-users] Backing up a BackupPC server, Les Mikesell
Re: [BackupPC-users] Backing up a BackupPC server, Les Mikesell
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