ONTAP Hardware

OK to convert a Flash Pool from RAID-DP to RAID4?


We recently purchased a FAS 2240-2 and FAS 2240-4 to replace our existing SAN, but I've got some time to play around and get familiar with them. Anyway, the SE that configured the systems for us really led us astray, and specified four 200GB SSDs in each unit to give us 400 GB of Flash Pool on only one of the heads in each FAS. We were told 400 GB is the current pool size limit.

What we didn't realize is that in the hybrid aggr, the SSD raid group must match the RAID protection of the HDD group, and since we went with RAID-DP, the SSD group must be RAID-DP. So one data, one parity, one d-parity, and one hot spare. This leaves us with only 200GB flash pool, and three SSDs just for RAID, ridiculous! I didn't know this until the installers came out and set everything up, and I'm still steaming from it. I tried to convince the installer that couldn't be the case, but he called several guys he works with and they said the console wouldn't let you do it if you tried, it must be RAID-DP, and it must have a hot spare.

But looking through some docs today, I saw that it may be possible to convert the SSD RAID group to RAID4:


Another option is to add the hot spare into the RAID group I think. But I'm afraid the system will complain about not having a hot spare. With RAID4, we'd have two data, one parity, and a hot spare, giving us the maximum 400GB flash pool size.

Any thoughts? Should I just leave it alone and deal with only having 200GB flash pool?



Robert -

I tried creating the mixed raid aggr on an 8.2 7-mode sim, and had success.

7m82a> aggr add test -t raid4 -g new -T SSD 8  

Note: preparing to add 7 data disks and 1 parity disk.

Continue? ([y]es, [n]o, or [p]review RAID layout) p

The RAID group configuration will change as follows:

RAID Group             Current           NEW           RAID Type

----------             -------           ---           ---------

/test/plex0/rg0        8 disks           8 disks        raid_dp

/test/plex0/rg1                        8 disks        raid4

I was also able to flip the raid type of the SSD tier back and forth from 4 to DP and back again:

7m82a> aggr options test raidtype raid_dp -T SSD

Aggregate test: cache raid group size is adjusted from 8 to 23 after changing raidtype.

7m82a> Fri Apr 18 02:33:29 GMT [7m82a:raid.config.raidsize.change:notice]: aggregate test:cache raidsize is adjusted from 8 to 23 after changing raidtype. 

Fri Apr 18 02:33:29 GMT [7m82a:raid.rg.recons.missing:notice]: RAID group /test/plex0/rg1 is missing 1 disk(s). 

Fri Apr 18 02:33:29 GMT [7m82a:raid.rg.recons.info:notice]: Spare disk v6.25 will be used to reconstruct one missing disk in RAID group /test/plex0/rg1. 

Fri Apr 18 02:33:29 GMT [7m82a:raid.rg.recons.start:notice]: /test/plex0/rg1: starting reconstruction, using disk v6.25 


7m82a> aggr options test raidtype raid4 -T SSD 

Fri Apr 18 02:33:47 GMT [7m82a:raid.rg.recons.aborted:notice]: /test/plex0/rg1: reconstruction aborted at disk block 43264 after 0:18.11 

Aggregate test: cache raid group size is adjusted from 23 to 8 after changing raidtype.

7m82a> Fri Apr 18 02:33:48 GMT [7m82a:raid.config.raidsize.change:notice]: Aggregate test:cache raidsize is adjusted from 23 to 8 after changing raidtype. 

Fri Apr 18 02:33:48 GMT [7m82a:raid.vol.mixed.raid.type:info]: test is now a mixed RAID type aggregate. 

Still not sure why the -T flag wasn't working for you earlier ?

I hope this response has been helpful to you.

At your service,

Eugene E. Kashpureff

Independent NetApp Consultant, K&H Research http://www.linkedin.com/in/eugenekashpureff

Senior NetApp Instructor, Unitek Education http://www.unitek.com/training/netapp/

(P.S. I appreciate points for helpful or correct answers.)

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