RAID 5 in new Mac Pro?

[twinsen]

I'm currently looking to set up a system based on the Mac Pro for editing and colour grading using Final Cut Studio 2 but can't decide what the best storage solution would be. I've been using macs for editing since 2000, but I'm new to RAID.

What I'm trying to decide on is if I should buy four 1TB internal drives for the Mac Pro and "connect" them using RAID 5 or if it would be better to keep one drives separate as a boot disk? SO:

1x1TB (OS) and 3x1TB i RAID5 (Video)

or

4x1TB in RAID5 (OS and Video)

In a RAID5 array would the 4 (or 3) drives show up as 2 (or 3) separate drives or would it show up as one massive? I'm aware that with RAID5 one drives is "lost" for parity information. From what I can tell, a 4 drive RAID5 would be faster then a 3 drive array? So what would be the major disadvantages with this set-up?

I'm also looking to get a 3rd party RAID card - any recommendations? The easier to use the better as I don't want to spend a week trying to figure out how to rebuild the array if one drive fails...

Sorry for the lengthy post - looking forward to hearing your replies!

Helge

 

[wh!plash]

Well, first of all, you can't boot off of a RAID volume (and you really don't want to).

You want your first disk in your MP to be your OS disk. Just a single stand-alone disk like it normally would be. This can be any size you want, and doesnt have to be the same as the RAID drives.

Then your other 3 drives can form a RAID volume. These 3 drives all need to be of equal size, otherwise they'll be formatted/partitioned to be the same size (limited to the size of the smallest one).

Like you said, RAID 5 gives you one disk's worth of redundancy. RAID 0 would just concatenate the drives together, but a disk or volume problem on any of the 3 would destroy the whole volume. The amount of performance increase you get by going RAID 0 is really not as much as some people think.

And to answer your question, yes, the 3 drives making up the array would mount on your mac desktop as one drive. If you open disk utility, you can see the RAID volume spanned across all 3 physical disks.

Oh and another thing, you'll gain performance going hardware raid (a card), but if the card goes bad, you'll have to have an identical card to read your disks. This is a big problem sometimes for old servers... Software RAID is just done in your mac by the OS. If you're OS dies, any installation of MacOS will be able to 'figure out' the volume and mount it. With a quad-core or octo-core Mac Pro, you've got the power to do a software raid without feeling any perfomance hit at all. If it were me (and i've got a mac pro quad), i'd run a software raid because its alot cheaper, flexible, and you wont see a performance hit.

 

[twinsen]

Oh and another thing, you'll gain performance going hardware raid (a card), but if the card goes bad, you'll have to have an identical card to read your disks. This is a big problem sometimes for old servers... Software RAID is just done in your mac by the OS. If you're OS dies, any installation of MacOS will be able to 'figure out' the volume and mount it. With a quad-core or octo-core Mac Pro, you've got the power to do a software raid without feeling any perfomance hit at all. If it were me (and i've got a mac pro quad), i'd run a software raid because its alot cheaper, flexible, and you wont see a performance hit.

Thank you very much for your reply! It's very interesting what you say about software RAID vs hardware RAID. But, what if one of the drives (in RAID5) fails? Would I use Disk Utility to rebuild and would it be a matter of replacing the dodgy drive, putting in a new one and click "rebuild"? (I know this is a very newbee question but my RAID knowledge is lacking)

Helge

 

[wh!plash]

Yep, pretty much. A RAID5 volume of 3 drives will have 1 drive's worth of redundancy. If one of the three drives went bad, you'd have to replace it with a drive of equal (or greater) size and use Disk Util to rebuild the volume and you'd be off and running. If another drive happened to go bad too (two out of the three) then yes, your volume would be long gone.

Basically think about it like this: with RAID5, every time your computer writes a 'piece' of data to the volume, it actually randomly writes that piece of data to TWO of the disks. So every single piece of data in the volume is in two places. So if any one of the drives dies, then you have a backup of every piece of that drives data on the other two. The 'rebuild' just takes all the pieces of data that only have 'one copy' and put them back a second time on the new disk. Thats a simplified version of it of course, but thats basically how it works.

With a RAID5 volume, your effective size of the volume is going to be (n-1)*S where n=number of drives in the volume and S=the size of the smallest disk.

So in your case, you'd have 3x 1TB drives that would have actual formatted capacity of 931GB (plus or minus). (3-1)*(931)=1862 or 1.86TB

 

[firestarter]

I would advise that you don't do it.

RAID 5 protects you against one thing and one thing only - a disk crash of one of the RAIDed disks. The benefit of RAID 5 is that you then keep your uptime, as you can rebuild the replacement while you're still online.

RAID 5 doesn't protect you from any other file lossage situation (accidental deletion, virus, corruption, theft, fire etc.). Specifically, RAID5 is not a backup!

In addition, RAID adds complexity and additional risks to your system. If you use hardware RAID, you have a risk that the RAID card will die and you'll need to replace it to get your data back. With software RAID you have more fears about corruption. It's expensive too - you're paying 50% extra if you buy 3 disks and get 2 disks worth of space. And you still don't have a backup.

If I were you (and this is what I have done), I'd buy 4x 1TB disks. Put 2 in your Mac - this is the 2TB of space that you were going to get from your RAID 5.

Take the other 2 and put them in external cases. Back up to these and maybe even leave them offsite. If you don't have 2TB of vital data, maybe back up the same to both, but rotate them.

This way you loose the complexity and make best use of your money - using it for backups - rather than protecting yourself against this single 'don't loose uptime following a single disk crash' scenario which is the ONLY thing that RAID5 protects you against.

 

[twinsen]

I'm aware that RAID is not a backup solution and it's not my primary usage for it at all. The reason why I want to use RAID5 specifically is to gain the speed benefit as I will be doing video editing, colour grading and compositing on high resolution video... Preferably I would do a RAID0 but that's just a bit to scary...

 

[firestarter]

I'm aware that RAID is not a backup solution and it's not my primary usage for it at all. The reason why I want to use RAID5 specifically is to gain the speed benefit as I will be doing video editing, colour grading and compositing on high resolution video... Preferably I would do a RAID0 but that's just a bit to scary...

I think you need RAID 0 for this. RAID 5 has a processing overhead.

If you have a full backup, you have nothing to worry about!

 

[Moof1904]

Is it true that you can't boot from a RAID volume? I thought I'd read in a past MacWorld article where they combined two drives into a Raid0 and made that the startup drive and showed that the performance boost to the MacPro was significant, albeit with risks...

 

[TJones]

Every hardware RAID volume I've ever met was bootable so I'm kind doubting on OS X not being able to boot off of a RAID set mentioned earlier.

On Raid levels; Raid 0 is fastest however there's no data integrity. If you lose a drive you lose the whole volume. If you're moving vast amounts of uncompressed video and need a fast scratch disk and are not saving any data to it then RAID 0 is for you.

If you want data protection but you want it low cost then RAID 5 is for you. Performance however is lacking since there is an overhead and additional writes necessary for each single unit of writes.

If you want speed and redundancy then go with RAID 1 (also called RAID 0/1, Raid 10, Mirroring) Every bit of data is written on two disks in case something goes wrong with one. Writes are only slightly slower (single digit %) and reads are potentially 50% faster (depending on how the sectors line up.

If you're going to bother doing RAID save your pennies and get a hardware RAID card. They have on board RAM that really helps speed up operations and preserves the data in cache in the event of a stoppage.

Finally, and most importantly, RAID doesn't mean you can go without backing up your data. Get yourself another drive just for backups (assuming you're trying to use Time Machine). It doesn't need to be fast but it does need to be large enough to hold your data. You can also go with tape backups if you want to go old school.

 

[matperk]

I think you need RAID 0 for this. RAID 5 has a processing overhead.

If you have a full backup, you have nothing to worry about!

RAID 0 is probably not what the OP is looking for. While it would be for video editing and all video would be on tape backups, if the raid failed (like my raid 0 did once) he would loose his project files and all the time he spent capturing his video and doing his color correction and other effects. If you wanted to do something like this, i would definitely recommend raid 5. If you were really serious about this, the best thing would be to get a small 4-6 drive raid system external to your MacPro--but they'll cost you.

Bottom Line: Do RAID 5.

 

[i3iz]

RAID 0 is probably not what the OP is looking for. While it would be for video editing and all video would be on tape backups, if the raid failed (like my raid 0 did once) he would loose his project files and all the time he spent capturing his video and doing his color correction and other effects. If you wanted to do something like this, i would definitely recommend raid 5. If you were really serious about this, the best thing would be to get a small 4-6 drive raid system external to your MacPro--but they'll cost you.

Bottom Line: Do RAID 5.

I have been booting off of RAID volumes in OS X for a couple years. Both hardware and software. However they are RAID 0 and RAID 1 (Stripe & Mirror) I have yet to setup a RAID 5, but i do plan on it.

Just wanted to dispell the myth. Also, my current setup is I think called RAID 10. It is 4 drives 2 sets of striped drives mirroring each other. It is very safe, if 1 drive fails, my computer just uses the other set of drives. And you would want to boot of it, because you gain a lot of speed from striped drives.