Expanding external RAID array

[cmmike]

Hi all - I have a virtual beer waiting for anyone who can help me with this

We have an external RAID array (running RAID 5), containing 3 HDs. Now I wish to add an extra HD. The RAID controller can support expanding the RAID - so hopefully i will just add the drive tell it to expand, wait for about 3 days and the jobs a good un ...

... but ... will OSX automagically detect that the drive has changed size? Can i just remount it and be happy? Or - will the new expanded RAID have to be reformatted (in the same way that it did when we first added it)?

any help very much appreciated

 

[fredk]

Hi,

I have just hit this self same problem. The answer is yes but...
First, RAIDAdmin will allow you to expand your RAID to include additional disks without destroying the data. (It is also pretty much instantaneous, esp if you check the RAID now button). This is clearly a good thing.

However, the BAD thing is that the Apple Partition Map does not currently support resizing of partitions, so your mounted volume will remain at it's original size, even though Disk utility will recognise the increased devlce size. For example:

/dev/disk4
#: type name size identifier
0: Apple_partition_scheme *1.8 TB disk4
1: Apple_partition_map 31.5 KB disk4s1
2: Apple_Boot 128.0 MB disk4s2
3: Apple_HFSX Data 1.4 TB disk4s3

(Total device size: 1.8TB, Volume size 1.4TB)

There is a tech note about this here: http://docs.info.apple.com/article.html?artnum=301443

A conversation with apple tech support suggested that if you originally formatted your RAID volume using the GUID partition map (under the partition options in Disk Utility) or as UFS (unix file system) or the dreaded MS-DOS (beware of potential (FAT32?) file size limitations here - have had problems over 1Gb i seem to remember) then it will work fine... Obviously this is what we have all done, right? Obviously this is what it suggests you do in the X-Serve RAID user manual, right?

If you had used GUID (and/or are using an Intel Mac) then I believe you can try something along the lines of

hdiutil resize -sectors max /dev/disk4s3

or something similar, but i have had no luck as we have a G5 X-serve... (see man hdiutil for more details...)

If I figure out how to do this without reformatting, then I will let you know directly. In the meantime, good luck!

Yours in sympathy,

Fred.