RAID-5: Using different size harddisks: best options ?

[maartenschool]

server: Dell Poweredge 2500 met PERC 3Di RAID controller
3 drives in RAID5 configuration
softw.: Win2000 server
To be added: 2 x 36 Gb

We want to extend our RAID5 virtual disk with 2 new disks but can't find a helpfile 'how to'.
We already placed and initialised the disks. After that it looked quite easy: Use Dell OpenManage Array Manager of Veritas, select the virtual disk and reconfigure. But, is it save to do it this way. The two new drives are twice as big (36 Gb) as the already existing drives (18Gb). As far as I know in this configuration it's only possible to use 18Gb/drive.
At the moment the virtual disk is still basic. Should we first upgrade it to dynamic and won't this disturb the functioning of the server?
What are the essential points to consider before reconfiguring the virtual disk. What precautions should one take? Does anyone have tips or tricks?

Thanks in advance, Douwe

 

[NickFerrar]

You can include the new larger disks into the existing array but it will only use 18GB from each of them. Are the speeds the same? In theory you can also mix speeds and the array just runs at the slowest rpm but in reality this can cause more issues than using different size disks. The correct method to include them is the one you mention, via Array Manager's recnfigure option. you can do it at the PERC BIOS level but the Array Manager GUI is friendlier

How are your partitions set up within the container? Do you have just a single C: drive or multiple partitions? If you have a separate data partition (e.g. a D: partition) then build the new disks into the array (it will take a few hours to complete although you can still use the disks in the meantime they'll be slower so do it out-of-hours if possible).

Once the RAID container includes the new drives then upgrade them to dynamic and extend the volume you want (other than C: which you can't do). You should also be able to do this with basic disks by creating a volume set but last time I tried that it didn't give me the option so I converted to dynamic disks without looking at it in detail (I was in a hurry!).

If you only have one partition currently (and you want the new space to be part of this partition) you'll need to use something like Partition Magic to extended it.

I haven't come across any side-effects from upgrading to dynamic disks so far. You'd only need to worry if you were dual-booting to an OS that doesn't support them. A client accessing a file on the server does so via the server's file access mechanism not it's own so it's irrelevant if the client supports dynamic disks or not.

As for precautions - can't do a lot apart from take a full backup really.

 

[xmario2013]

as far as I know Dynamic disk can be bad news for the system performance because it takes away process from the OS, that is the reason you have hardware RAID to take away the work from the CPU with its own

for RAID 5, you have to have all the same size hard drive or else its going to go down to the smallest size disk for the VD,

your best bet is to backup all the data onto tape or somewhere else and call up Dell to find out how to do this in the RAID manager