RAID 5 question

[[LYL]Homer]

I'm about to rebuild my media system and am planning to finally go RAID 5. I'm looking at an MSI K8NGM2-FID mATX (nVidia 6150) board with nVRAID capable of doing RAID 5. It has 4 SATA 3.0gb/s ports on the board. As I understand it this will be a software type RAID and not as fast as using a $300-ish hardware card to run the array. I plan on using Seagate's 320gb 7200.10 perpendicular tech drives.

My question is with this setup can I start with 3 drives in RAID 5, and then upgrade later by adding a 4th drive without losing data, or will the array wipe the data to rebuild? I figure that even if it could rebuild without losing data that there would be a higher than average chance that the process could corrupt and I'd have to start from scratch anyway. (I'd back up critical data in any case.) I'm just trying to figure out how much of a PITA factor I should allow for this.

I'd like to reduce the inital cost of the rebuild to limit the other PITA factor - the wife grousing about the htpc cost. (Yeah, she uses it even more than I do and was pissed after a drive went out recently and took all her favorite shows - PITA!)

 

[AtomicFire]

Most likely you will need to destroy then remake the array with the extra drive. What you are looking for is called Online Capacity Expansion, which is usually only available with higher-end controllers.

 

[dirtydr]

I have read references to an nvraid feature called morphing. Nvidia claims that you can basically perform OCE but google is silent about people adding capacity to a level 5. There are people claiming good results adding another disk to a stripe but that does not guarantee anything. Maybe try finding a whitepaper on the nvidia 430 chipset to see if it is explicitly supported.

 

[Madwand]

I have an Asus 430/6150 board (K8N-VM CSM) and as far as I can see, there's no way to increase the size of a NVRAID 5 array without a delete & re-create, with the current nForce drivers, version 8.26. In fact, there isn't even a way to create a RAID 5 array using the Windows utility ("Media Shield") -- you have to do that from the BIOS. There's no way to migrate that to another RAID 5 array in Media Shield, and no way to increase the space via the BIOS. This looks like an issue that might be dealt with via nVIDIA support, but I wouldn't count on it. Pre-sales, BTW, is a great time to take up the question; I've personally had good experiences dealing with NV pre-sales online.

I can however create a RAID 0 array of a couple of drives, and migrate that to a RAID 0 array of greater size. So it looks like a RAID 5 software issue. (As usual, the partition size stays the same and needs to be expanded with some other tool after the underlying array migration is done.)

In any case, I'd say, that doing any sort of capacity expansion without a full backup is very risky. There are at least 3 points of failure here: (1) error during hardware re-configuration (2) error during array re-configuration (3) error during file system re-configuration. Moreover, steps (2) and (3) generally take a very long time to finish, and in that time, if you have a crash, power failure, switch off, cable come loose, etc., etc,. I think you could be in trouble. IMO, online capacity expansion should not be done without a backup; it's an up-time increasing tool, and not a facility that you should use to avoid a backup.

(I'm not even sure that it saves much time overall; in some cases, a recreation and restoration from backup takes less time than an inline re-configration -- the inline re-configuration goes through all the drives; a backup restoration will only go through the data space actually used. It's definitely true right now, when I have a mostly empty array for testing -- re-configuration will take hours; re-creation and "restoration" would take minutes. And that backup gives so much flexibility and additional reliability...

In addition, spanning/JBOD also strangely doesn't support the "migrate" function for capacity expansion. I did manage to delete and recreate that array while preserving the partition, and it seems OK, but I don't like doing it this way.

The NVRAID feature set is fairly strange, so please don't take my post as definitive -- if you really really want some feature, you should double-check with NV support or pre-sales.