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37 Posts
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1577
June 2nd, 2017 02:00
Backups and config - where?
Hi all
I've an open call with EMC for this, but the answer they keep giving is "the MDMs have the config and it's constantly changing, there's nothing to back up!".
I've gone back to them with:
I’ll put it another way – if the entire cluster is powered down, then when I reboot it, it will have to somehow know how to reconstruct the cluster. Given that what was in memory of the MDMs has clearly gone (as they were powered off), somewhere, something has to hold data/config so ScaleIO can go “ah yes, a 14 node cluster, using these disks, providing these volumes – now I remember!”.
For example, does each SDS node hold the config in metadata on the disks, and they use this to present their own config to the MDM cluster, which is then created in memory as nodes join? This is critical that we know this, for DR purposes.
Does anyone have any input here? How is the cluster formed, from a complete power-down situation, where is the base config pulled from and how does everything come up to a good state again?
Thanks
AW
pawelw1
306 Posts
2
June 5th, 2017 07:00
Hi Andy,
Basically, the MDM configuration is stored in a repository file which is synchronized between the MDM nodes. When the cluster is coming up, the MDMs will contact each other, determine which one has the most recent (valid) version of the repository, reconnect SDS's etc.
There is no point in copying the repository file though - as my colleagues say, the configuration (i.e. SDS chunk mapping) is constantly changing, so even a valid copy of the repo becomes invalid in a matter of seconds - best is to let ScaleIO take care of the repository.
Can you PM me the SR# so I can look closer into it?
Many thanks,
Pawel
andyinv
37 Posts
0
June 5th, 2017 08:00
Thanks Pawel
I did understand that it was constantly changing, but you know what it's like - someone decides "they have to have the config backed up" and so you have to give them something as a tick in the box. Is there no metadata written to the disks or anything that aids in resurrecting the config, it all comes from the repository file? Which is the file (wintel), incidentally?
Will PM the sr.
Thanks
A
pawelw1
306 Posts
0
June 7th, 2017 03:00
hi Andy,
If it's only about "checking the box", you can backup /opt/emc/scaleio/mdm/rep/mdm_rep.bin file - but again, in case of restore from that backup, you will most likely face a partial DL, as the chunks mapping will change. It's surely better to have something rather than nothing, but it's simply not the way of doing that. Maybe you could think of copying whole MDMs "images" to the DR site?
Cheers,
Pawel