Re: [Moosefs-users] Backing up MFS metadata

[Michał B. <mic...@ge...>]

Please read this article: http://www.moosefs.org/news-reader/items/metadata-ins-and-outs.html

 

The most important part for you is here: 

The metalogger will download the metadata.mfs.back file on a regular basis (by default every 24 hours) from the master server. The downloaded file is saved with the file name metadata_ml.mfs.back. Similarly, it also continuously receives the current changes from the master server and writes them into its own text change log named changelog_ml.0.mfs. Where these files are also rotated every hour up to the configured maximum number of change log files (see man mfsmetalogger.cfg).

 

Yes, you can fully restore metadata from files saved by metalogger.

 

If you need any further assistance please let us know.

 

 

Kind regards

Michał Borychowski 

MooseFS Support Manager

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Gemius S.A.

ul. Wołoska 7, 02-672 Warszawa

Budynek MARS, klatka D

Tel.: +4822 874-41-00

Fax : +4822 874-41-01

 

From: Roast [mailto:zha...@gm...] 
Sent: Friday, July 16, 2010 1:45 PM
To: Michał Borychowski
Cc: Stas Oskin; moosefs-users
Subject: Re: [Moosefs-users] Backing up MFS metadata

 

Another question.

Does master server sync the change log to metalogger server in real time?

And if so, we can restore the full meta info from the metalogger server. Am I right?

2010/7/15 Michał Borychowski <mic...@ge...>

You can backup changelog files (you would need just the two newest ones – “0” and “1”). You can make these backups even every minute. So you can have potentially lost information for about 1-2 minutes.

 

But the question is – why to back up changelogs manually? Metalogger machines are dedicated to this. You can have as many metalogger machines on the network as you like. And metalogger process can be run on any computer, even an older one. 

 

 

Regards

Michał 

 

 

 

From: Stas Oskin [mailto:sta...@gm...] 
Sent: Friday, July 09, 2010 2:27 PM
To: Fabien Germain
Cc: moo...@li...; Michał Borychowski
Subject: Re: [Moosefs-users] Backing up MFS metadata

 

Hi.


As for the time it takes, it depends on the number of chunks you have, and the hardware server you use (CPU + HDD speed). For example in our case (15 million chunks, 6 GB of metadata), it takes between 1 and 2 minutes on a Xeon processor.


I actually meant, how much time backwards could be recovered by replaying all the logs?

Michael said that backup log is created every hour so up to 1.5 hour can be potentially lost.
If all the logs are replayed, can the data be consistent up to the moment of crash?

Regards.


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