We've got an F740 with three shelves of 36GB disks (the 3rd recently added).
We've only got one volume, vol0, with 14 disks in it now (13 data and one parity). We use both CIFS and NFS. We have 7 spare disks (6 of which we'd like to eventually use for data, with one spare of course).
I just went to add one of the spare disks to vol0 (running low on space) and got the error:
vol add: starting a new RAID group; at least two disks are needed
So, as I (now) understand it, we've got to either:
- Override the 14 disk limit for a RAID group
or
- Add a new RAID group to the current volume
or
- Add a new volume
The 3rd choice is unattractive because we like the idea of One Huge Filesystem, that we can divvy up as needed into different qtrees.
The 2nd choice sounds like a Bad Idea in that according to this document, section 3.4: http://www.netapp.com/tech_library/3027.html, that the filer will try to distribute writes evenly between the old and new RAID group... if the new RAID group only contains two disks (we don't want to add more disk space than is needed now), this could be disatrous to performance
So is the 1st choice, increasing the size of the RAID group, a viable option? What is the downsize? Only increased risk of a double disk failure taking out the whole system? Is it possible to add a second parity disk to the same RAID group?
Am I missing something here? Any clue-by-fours quite welcome.
thanks
johnS
John,
Just a couple of remarks: I'm sure others will have had more practical experience.
So, as I (now) understand it, we've got to either:
- Override the 14 disk limit for a RAID group
I'm a little intrigued that you have it set to 14 (with the implication that you haven't had to increase it before). The default for new volumes has been 8 for some time now. Is this is a volume that was first created long ago, or are you (pardon the suggestion) still running an ancient ONTAP version?
The 2nd choice sounds like a Bad Idea in that according to this document, section 3.4: http://www.netapp.com/tech_library/3027.html, that the filer will try to distribute writes evenly between the old and new RAID group... if the new RAID group only contains two disks (we don't want to add more disk space than is needed now), this could be disatrous to performance
This is a real problem with growing a volume gradually: it's _never_ the right time to start a new RAID group :-(
Since 6.2(iirc) it's been possible to add new disks to any RAID group in a volume, not just the last one. So if you've had the foresight to have started with the right number of RAID groups, you can add disks to them round-robin. Not much help in your situation, though.
Is it possible to add a second parity disk to the same RAID group?
In 6.5, you can use DP (double parity), see the reference that Steve Strange posted here a couple of months ago:
http://www.netapp.com/tech_library/3298.html
At first glance, that seems to me like the least bad solution for you.
Chris Thompson Email: cet1@cam.ac.uk
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Chris Thompson -
Stewart, John