mdadm or 3ware hardware raid

[skyking]

I am building a PACS archive server for a small business. I'll use a pair of small drives on hardware raid 1 for the OS, and either a raid5 or raid6 for the database and images.
Is it easier to grow mdadm than it is a hardware card?
The I/O will not be a problem on this setup, so offloading the work to the hardware card is not the issue.
I will start it out with 1.5~2 TB and will probably need to grow it at some point in the future.

 

[Brazen]

Personally, I would probably mdadm just because I am familiar with it.

 

[Nothinman]

You can grow Linux software RAID volumes while the OS is running, I'm not sure if the card will let you do that. And you'll be able to move the software RAID volume to any other controller without a backup/restore step.

 

[acaeti]

Growing RAID is a pain in the ass either way.

Hardware RAID, you generally need to grow from the card's BIOS and it can take hours (sometimes many hours if you have many disks) to grow a RAID 5, so that can be quite a bit of downtime, and if there is a fault while growing the RAID5, well let's hope you backed up.

Software RAID for Linux I believe it is best practice to unmount any volumes from the md device before attempting to grow a RAID5. So that is downtime too, and same rules apply for a muffed expansion.

I think the best idea is to setup an initial RAID5/6 and run LVM on it. Then, as your needs grow, add an additional RAID5/6 md device and add it to the LVM pool. You lose a little bit of disk space compared to one large RAID with all disks, and you have to add disks in batches, but you gain a little more fault tolerance and a lot of ease-of-use and ease-of-expansion.

If there is not going to be a lot of disk load on this system, then I would recommend a software RAID solution as you can save a few bucks, no matter if you choose to expand it by adding disks to the existing RAID or adding RAIDs to an LVM.

 

[acaeti]

Oh yeah, and I second the "move the software volume to any other controller". It can be a pain to have an expensive hardware RAID card go sideways, then have to wait for a replacement.

 

[skyking]

I was leaning toward software for those reasons, but moving the disks to another controller/system is daunting to say the least. Has anyone here had to do that IRL?
Is it a simple discover process? I can google up the whole shebang, just looking for a quick explanation.

 

[Nothinman]

Each disk in an MD has a RAID superblock and UUID so moving them around shouldn't require any work on your part, IIRC.

 

[Crusty]

I've moved several array's in a LVM from computer to computer before. Just make sure that the new computer knows to search for LVM devices and you should be good to go.

 

[Nothinman]

There's also the fact that you can add disks from other controllers into the RAID set, so once the 3Ware gets full you can add another card or use the onboard controller to house disks in the array.

 

[skyking]

I'm sold
I'll grab enough disks for initial deployment, and plan expansion using a second controller and a follow-on raid set. LVM will make it transparent.
Anyone set up software raid with a hot spare on linux?

 

[child of wonder]

Where I do consulting I set up a simple file server using RAID 1 for the OS and RAID 5 for the file share with LVM on top. Expanding the RAID5 array shouldn't be too bad if they ever need to increase space but they only use 185GB out of an available 550GB.