I agree with Tom. Your best bet is to add 6 disks to a new raid group. No sense in having all those spares sitting around doing nothing. I would try to avoid expanding a 36GB-disk raid group past 14 disks for reliability.
Moshe Linzer IT Manager National Semiconductor, Israel Phone: 972-9-970-2247 Fax: 972-9-970-2001
"Yarmas, Tom" Tom.Yarmas@netapp.com Sent by: owner-toasters@mathworks.com 04/06/2004 04:19
To: "Stewart, John" johns@artesyncp.com, toasters@mathworks.com cc: "IT Technical Services" ITTech@artesyncp.com Subject: RE: Best practices for new RAID group
The paper you reference is a little dated unless you are still running 5.x of Data ONTAP. Data ONTAP version 6.x included some significant changes to the WAFL and ONTAP RAID.
The number of RAID groups is much less relevant than the total number of data drives in the volume. However, adding 1 or two drives to a volume (or RAID Group) is still not the best approach.
Your best bet is to add a new RAID group of 6 disks to the volume. You will be adding the disks anyway (over time), and you are using qtrees to divvy up the space, so just add them all at one time and not worry about it.
As Chris Thompson pointed out you can use RAID-DP (assuming you are running DOT 6.5), and add 2 disks to the existing RAID group. But that would likely not be optimal because you would still have a small number of "empty" disks in the RAID group and they will be utilized more than the other "more full" disks until space gets more evenly distributed across all of the drives.
-tom
-----Original Message----- From: Stewart, John [mailto:johns@artesyncp.com] Sent: Thursday, June 03, 2004 5:44 PM To: 'toasters@mathworks.com' Cc: IT Technical Services Subject: Best practices for new RAID group
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