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Enabling NR10 on a overprovisioned LUN

silus
Advisor

Enabling NR10 on a overprovisioned LUN

Hi,

I just wanted to check my understanding before I tried this change.


We have a lefthand cluster totalling 16TB usable. There is a 10TB thin provisioned Lun with about 700GB data on it.

 

If I enable NR10, it won't duplicate the lun and then bring it offline because the totalled 20TB is larger than the 16?

 

Will it just show the usage is double the original used amount or will it show in the console I am overprovisoned at 20TB?

 

thanks

5 REPLIES
oikjn
Honored Contributor

Re: Enabling NR10 on a overprovisioned LUN

if your thin provisioned drive is only consuming 700GB currently (in NR0?!?!?!), then when you convert it to NR10, you will consume 1400GB.

 

 

silus
Advisor

Re: Enabling NR10 on a overprovisioned LUN

Thanks. it is consuming 700GB in NR5.  So it is safe then to enable NR10 and it will only then double the amount of required space regardless of the amount of provisioned space the lun will remain up, I just have to keep an eye on the amount of used space that it does not fill up and cause the lun to go offline

 

Is the 'Consumed Space' metric on the volume in the CMC inclusive of parity?

oikjn
Honored Contributor

Re: Enabling NR10 on a overprovisioned LUN

I haven't really played around with NR5 so I don't know for sure, but I would guess it does include parity in that value.

 

Either way, if you have ~700GB in NR5 and 10+TB free, I'm sure you will not run into any issue with migrating to NR10. 

 

One thing I make sure I do on my system is keep a "system reserved" LUN on my VSAs that is just a blank LUN fully provisioned so in a pinch if I screw up and fill up the VSA system though some error I can always get a quick boost of free space to get my production LUNs back online in RW mode.

silus
Advisor

Re: Enabling NR10 on a overprovisioned LUN

That is a very very good suggestion. What size reserved LUN do you suggest to create?

oikjn
Honored Contributor

Re: Enabling NR10 on a overprovisioned LUN

It would be up to what you think is appropriate to your environment.

 

It would depend on what kind of buffer you want.  In my case I have a 200GB of "reserve LUN".  The reason I went with that size is that it was enough that if one of my overprovisioned LUNs goes crazy and fills up my system, I could turn off the offending LUN access and instantly get more free space to give the rest of the LUNs RW access and then migrate the data off of the bad LUN and back into a new LUN without having to worry about filling the system before everything is complete while the system is experiencing its normal growth rate.

 

On the other hand...  IF I was getting close to the point of needed another node to add in and was putting it off until the absolute last minute, I would probably make the reserve LUN a bit larger so that once I deleted that I would have enough time to get a new node ordered and installed before the system filled up again.

 

 

In my case, I could probably get away with a reserve of less than 50GB without issue since our data growth per week is <2GB (or 4GB when translated into NR10), but I have the excess capacity so I figure slightly larger is better as long as I can afford the lost space.  I also keep the reserve LUN in NR10 because I find the warning about NR0 to be annoying.

 

 

It all depends on what you feel comfortable with, but I highly suggest having something in there since the moment the VSA system fills up all LUNs go Read-only and that tends to break most systems.  I had it happen to me once when I didn't have a spare LUN and suddenly I had to make some quick decisions on what I and to delete ASAP to get the system back up and running and deleting snapshots takes a while before you get that space reclaimed so I ended up deleting my smallest LUN (my cluster quorum disk) to get the rest back online and then it was a careful juggling act to get everything sorted out live.