What RAID is Better for my Use

[berwicke]

I"m going to run a RAID array in my mac pro. Currently i have two 500gb seagates in a software level RAID for 1TB of striped storage. It is still a bottleneck. What is better? a Three Disk RAID 0 with 1 Disk backing up via Time Machine; A Four Disk RAID 4 with parity on one disk; a Four Disk RAID 5 with the striped parity; or going external with a RAID array using ESATA and Velociraptors, but keep in mind this is for Video Editing so i won't need to take the files anywhere and would prefer the cleaner internal setup.

 

[palladin9479]

Ok you need to answer a bunch of questions first. One being what kind of disk controller are you using? If your "RAID" is software RAID with the CPU expected to do the XOR parity calculations then you shouldn't expect performance from a RAID 3/4/5 array, the I/O's to and from the CPU will kill performance no way about it. If your doing video editing then it goes double as your CPU will most likely be at its busies when those I/O's need to be processed. If you have a real RAID controller then the card should have its own XOR coprocessor for this. Somehow I really doubt you have a real HBA, their pretty rare on consumer systems.

Most likely your going to want a 4-member RAID0 striped array. User an external disk to maintain backups of your most critical data. ESATA is just an exported SATA connection, it will only support a single disk attached. Your external enclosure would then have to do one of two things. One is provide something called a Port Multiplier "PMP" preferably in FIS mode. These are common for SAS backplanes and other disk arrays for servers, and many enclosures have them also. Your HBA will need to support PMP in FIS mode else the port multiplier won't work. The other method is that the enclosure has its own firmware doing RAID and exports the drive array as a single array to the HBA. This is more common but the performance varies from enclosure to enclosure due to them using diffing XOR co-processors, and enclosure websites rarely tell you which one their using.

 

[berwicke]

Ok you need to answer a bunch of questions first. One being what kind of disk controller are you using? If your "RAID" is software RAID with the CPU expected to do the XOR parity calculations then you shouldn't expect performance from a RAID 3/4/5 array, the I/O's to and from the CPU will kill performance no way about it. If your doing video editing then it goes double as your CPU will most likely be at its busies when those I/O's need to be processed. If you have a real RAID controller then the card should have its own XOR coprocessor for this. Somehow I really doubt you have a real HBA, their pretty rare on consumer systems.

Most likely your going to want a 4-member RAID0 striped array. User an external disk to maintain backups of your most critical data. ESATA is just an exported SATA connection, it will only support a single disk attached. Your external enclosure would then have to do one of two things. One is provide something called a Port Multiplier "PMP" preferably in FIS mode. These are common for SAS backplanes and other disk arrays for servers, and many enclosures have them also. Your HBA will need to support PMP in FIS mode else the port multiplier won't work. The other method is that the enclosure has its own firmware doing RAID and exports the drive array as a single array to the HBA. This is more common but the performance varies from enclosure to enclosure due to them using diffing XOR co-processors, and enclosure websites rarely tell you which one their using.

ahh thank you very much! yes i'm running software level RAID so it will tax my processor quite a bit i bet so i probably should go with the 4 disk RAID 0 its probably the best idea. how expensive would a RAID controller run me, i'd love to get one as i have one free PCI Express slot but i'm on quite a budget so if i can get a four SATA one for seventy or eighty dollars then i'll definetely do that and if i did get a RAID card then which would you recommend RAID 4 or RAID 5. If not then i'll do what you said and get four 1TB Disks in RAID 0 and use my dual bay firewire 800 enclosure with two 2TB in RAID 0 for backup. But what i would like to know is in your opinion do you think it's wise to use that RAID array for OSX and my applications as well as my video files? i always thought that you should keep your OS and apps on a seperate drive than your assets but i guess with a backup i shouldn't really worry. redundancy is really my biggest concern though. i don't have redundancy right now with my current setup as my time machine skips over a lot of files because i don't have enough room and it keeps extra versions of each file which i don't want, i just need to most recent version. So if i did get a RAID card with it's own XOR processor and ran a parity RAID should i run RAID 4 or 5 and what is RAID 3?

 

[palladin9479]

Dedicated real HBA's run 200 ~ 500 USD depending on options. And while some "cheap" ones do exist you'd be better served by avoiding them due to their low performance. Highpoint and Adaptec make some nice high quality RAID HBA's that do SATA 3 and 6.

If you have a high quality card then you can do RAID5 with 4~5 disks and be perfectly ok. The card will take care of all the math work, the host OS just see's a super fast single large disk.

 

[berwicke]

thank you very much i'll have a month or two to decide which i want to do a four disk RAID 0 at the software level, or a hardware RAID 4 or 5.

 

[FireWire2]

If you need a quiet external box can delivery 240MB/sec for your FC then get this five bay hardware raid driver-less

 

[tokencode]

I would recommend none of the above and go with a 4 disk RAID 10 if you are buying 4 disks....

 

[Pyree]

I will go for option 1 as I voted because it give you the fastest speed and since I don't think a hdd will die every day, you don't really need the mirroring function of the raid10.

 

[berwicke]

thanks for all the great info guys! i think i will go with my first option too but eliminating the fourth 3tb drive and putting in a fourth 1 tb drive for a four disk RAID 0. reason being in the last week i have reconfigured my drives so my two disk RAID 0 is for current stuff and everything that i'm done with is on the single 1tb drive. i've found that this way i can store things on a reliable hitachi drive that shouldn't die soon considering it gets almost no workload at all as a long term storage drive only. that way if a disk does die and being RAID 0 i'd have no way to rebuild, i only lose my imcomplete work. plus i remember i have an OWC merucy elite al pro dual sata firewire 800/400/USB2.0 RAID 0 enclosure that i could always slap two 2TB in to use as backup.