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How much redundancy do i have ?
Hi All
I have an environment with 12 nodes. Each node is in its own fault set and i have spare capacity of 10%
I would like to know in what cases would i get into trouble
If two hosts go down at the same time , is that a problem ?
If i were performing maintenance on one host and i placed that sds in m-mode, if another host went down at this time, would that cause issues ?
Basically i want to build as much redundnacy as possible into host failures
Thanks
Anonymous
5 Practitioner
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November 27th, 2016 14:00
Hi mickhooly,
Just to compliment the latest answer by Pawel - the rebuild doesn't start during m-mode, as the purpose of the m-mode is to keep 2 copies of your data during the time of nodes/fault sets in m-mode with minimal IO penalty.
Once the SDS/Fault set exits m-mode - we will rebuild in order to "compliment" the data it missed while being in m-mode.
I hope this further clarifies the issue.
Thanks,
ItaiR
pawelw1
306 Posts
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November 18th, 2016 00:00
Hi Mick,
Basically, with two SDS going down at the same time, you are facing a DU situation. It applies to a single Protection Domain, so if you have more than one, you can survive single SDS failure in each PD at a time.
When one SDS is in the maintenance mode (and the rebuild has finished), you can disable another SDS in the PD, but please remember that you might run out of space if you shut down too many of them simultaneously, so just keep that in mind.
Hope that helps - let me know if you have any other questions!
Pawel
mickhooly
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November 18th, 2016 02:00
ok i have been doing maintenace recently and when i put the sds into maintenance mode the rebuild doesnt happen until the sds is taken back out of m-mode
pawelw1
306 Posts
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November 18th, 2016 02:00
DU = Data Unavailability; basically you might not be able to access some of your data.
Fault Sets logically group SDS that have a high chance of failing at the same time - typically, SDS located in the same physical rack (there's a chance that all of them will go down together due to power failure etc.) - so ScaleIO knows not to put both copies of the data in the same Fault Set.
Please check out "Fault Sets" section in ScaleIO UserGuide for more details on these.
Cheers,
Pawel
mickhooly
23 Posts
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November 18th, 2016 02:00
sorry, DU?
And what is the purpose of fault sets ?
pawelw1
306 Posts
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November 18th, 2016 03:00
Well, in theory there shouldn't be any rebuld when entering the maintenance mode, but basically every time you do something with the SDS it's better to have a look at the GUI and make sure there's no rebuild/rebalance going on, just to be on the safe side.