HW RAID 1 different disk sizes?

I was told by an HP support guy that I should not replace a failed drive in a mirror with a bigger size drive, since it could crash my array.

I am puzzled why is this so and how to hell am I suppose to support this array once the specific hdd model is not available any more?

Solution 1:

There's a big difference between "It should work" and "It will work" and if I was that HP guy I'd have gone with the first statement too, if he'd gone with the second and you'd lost data he could have been in trouble. That said 'it should work' :)

Solution 2:

Unless there's some specific bug in the hardware, all putting a larger drive in the array will do is make the space beyond the size of the smaller drive unused/unusable.

Solution 3:

You should not mix speeds and sizes of drive for a very specific reason:

In an array the entire drive moves at the slowest speed drive speed and errors are over 30 percent more likely on non-matching drives (not because of physical limits but because the writes don't queue, or don't queue the same)

As the addendum, Required up time is the best measuring stick. If you need 5 nines (99.999) of up time, match all the way to the batch number. for 4 nines match make, size, and speed, for 3 nines i would still match make speed and size. for 2 nines i match speed and for anything lower i don't really care.

If your not sure what 5 nines is. On a windows box imagine at least a 3 way cluster, split across geological fault lines with redundant ISP's at each site, Any updating software like windows updates are kept turned off until they are tested in a matching test lab and applied on a 2 for 1 rolling update schedule. At this level you can afford a new array when you loss one drive.

Solution 4:

OEMs almost never recommend putting different sizes or speeds in an array together. But you can definately do it, unless as already stated the OEM has a bug or "feature" that prevents it.