ServeRAID M5015 Controller upgrading hard disks without downtime or data loss

RAID-5 is a fault-tolerance solution, not a data-integrity solution.

Remember that RAID stands for Redundant Array of Inexpensive Disks. Disks are the atomic unit of redundancy -- RAID doesn't really care about data. You buy solutions that employ filesystems like WAFL or ZFS to address data redundancy and integrity.

The RAID controller (hardware or software) does not verify the parity of blocks at read time. This is a major risk of running RAID-5 -- if you encounter a partial media failure on a drive (a situation where a bad block isn't marked "bad"), you are now in a situation where your data have been silently corrupted.

Sun's RAID-Z/ZFS actually provides end-to-end data integrity, and I suspect other filesystems and RAID systems will provide this feature in the future as the number of cores available on CPUs continues to increase.

If you're using RAID-5, you're being cheap, in my opinion. RAID 1 performs better, offers greater protection, and doesn't impact production when a drive fails -- for a marginal cost difference.

Yes... This is possible. So you're saying you have 7 disks in the RAID 5 set, and want to take disk #8, which is currently a spare, and move it to become the 8th member of the RAID 5 array?

If you have the HP Array Configuration Utility (HP ACU) installed, this is very easy. There is a web-based GUI and a command-line option to handle this change. It can even be done online without taking the server down, as long as the right things are in place.

We would need to know the server model, controller type, cache configuration and operating system to be able to give specific details/actions.

A generic CLI setup using the hpacucli utility:

=> ctrl all show config

Smart Array P400 in Slot 9    (sn: P61630D9SUI2C3)

   array A (SAS, Unused Space: 0 MB)

      logicaldrive 1 (410.1 GB, RAID 1+0, OK)

      physicaldrive 1I:1:1 (port 1I:box 1:bay 1, SAS, 146 GB, OK)
      physicaldrive 1I:1:2 (port 1I:box 1:bay 2, SAS, 146 GB, OK)
      physicaldrive 1I:1:3 (port 1I:box 1:bay 3, SAS, 146 GB, OK)
      physicaldrive 1I:1:4 (port 1I:box 1:bay 4, SAS, 146 GB, OK)
      physicaldrive 2I:1:5 (port 2I:box 1:bay 5, SAS, 146 GB, OK)
      physicaldrive 2I:1:6 (port 2I:box 1:bay 6, SAS, 146 GB, OK)
      physicaldrive 2I:1:7 (port 2I:box 1:bay 7, SAS, 146 GB, OK, spare)

In this case, I could remove the spare with: ctrl slot=9 array A remove spares=all

I could then add the now unassigned disk, physicaldrive 2I:1:7, to the existing array with:

ctrl slot=9 logicaldrive 1 add drives=2I:1:7

or

ctrl slot=9 array A add drives=2I:1:7

The difference is that the first would add to the existing RAID 1+0 logical drive (which doesn't make sense since it's an odd-number of drives). The second would result in the array being larger and would give that array 146GB of "unused space", which could then be carved into another logical drive.

You can have different RAID levels on HP logical drives contained on the same group of disks!

In your case, the first command would just expand your RAID 5 array. In Windows, the space would become available. In Linux, it depends...

Edit: The OS is VMWare ESXi 5...

Your options are to run this from the bootable HP SmartStart CD using the GUI or you can install the HP ESXi bundles (here and here) for ESXi and get a usable hpacucli command-line interface to run from an ESXi console. It requires a reboot.