Basically the difference is dedicated parity (3) versus distributed parity (5).
Controller cards for raid3 are more difficult to make than raid5 controllers. Only Areca makes them.
The second difference, resulting from the first, is that if a drive ever fails, a RAID 3 will keep most of it's performance during a rebuild, whereas a RAID 5 will slow down noticeably, possibly to the point where you couldn't edit while it was being rebuilt.
The third difference is that with large file sequential reads/writes (which is what video is all about), RAID 3 is faster than a RAID 5.
Thanks harm and jim for the explanation, things are a lot clear now.
The performance drop during rebuild is not nearly as bad as described or as bad as it use to be if you have an Enterprise Level Raid controller instead of the onboard. Background rebuild and initialization lets you decide what % of the controller cpu is set to rebuild and what is set to operations. By default that is 20% to rebuild which is very little overhead on the card. Rarely are you using over 80% of the card's cpu during operations. I have a client who records from 14 different security cams on a 5 drive raid 5. These security cams are constantly starting and stopping based on motion. The stream being recorded is H264 or motion jpeg. The raid handles that load without issue while rebuilding since they had a drive failure.
The drive performance is correct for sequential files but it's not nearly as significant anymore with the changes to the way raid 5 is handled by the controller. Raid 5 arrays give you good performance for asyncronous or syncronous file operations. Overall it's the cost involved and tha raid 5 controllers are cheaper. Raid 6 is also better security and gives you close to the same performance as raid 5. You may want to consider that as well.
So in terms of pure performance Only, let's say in a 6 disk setup ( c= os, apps one 300 gb / d = media, projects, pagefile, etc.... 5 x 2tb seagate ) the speed of the system will be just about egual, or more than 20%.
To be honest if i can save some money in this build i'll take it.
The drive performance is correct for sequential files but it's not nearly as significant anymore with the changes to the way raid 5 is handled by the controller.
Any chance you have some published benchmarks, Eric? The one's I've seen show a different story (RAID 3 being significantly faster than RAID 5 on the same card), but they are a bit old. Things may well have changed, and I'd love to see some new benchmarks.
very little difference in performance if any now, 3 is too costly for what little
gains you may have.
guess we have to run some benchmarks again.
3 is too costly for what little gains you may have.
Why is that? The overhead in terms of disks is the same as 5, so there is no extra cost there. Controllers from Adaptec, Atto, 3Ware and Areca do not differ much in price (12+ port versions) and often Areca is a little bit less expensive, so there is no cost diference there either.
One thing that is a distinct and clear advantage of Areca over other controllers is the ability to expand the cache memory to 4 GB, where all the other brands are limited to 512 MB.
The controllers we use most of the time do not support raid 3 so I can't verify the 2 raids on the same controller. I compare benchmarks reported by others with raid 3 to the Intel with raid 5 and the results are not that far apart. These benchmarks were run when the Intel card when they first released. The performance now is better after optimizations.
Average transfer rate. Burst was over 1000mb/s
Intel SAS RS2PI080 8 Port controller with 512 DDR2 Ram
8 Drive Raid 5 - 745MB/s read 735MB/s Write
8X WD 1TB SATA 6 Gb/s, 64 MB Cache, 7200 RPM
8 Drive Raid 5 - 703.8MB/s read 670MB/s Write
Revised: Sorry for some reason the last part of the copy kept getting cut off
the onboard ram has little to do with large file transfer once loaded its loaded. the onboard ram is about high transaction iops.
(server style multiple request). not video editing.
so added ram is a moot point in large file transfer, unless you do the no no of having your drives more than 60% full then it comes into play again.
you left out Intel.
12+ ports? now you are in the less than 5% of adobe users at best.
8 port cards are what most would buy. (also in the minority)
cheapest 8 port Sata 600 Areca $1049 (only one that does raid 3) ever wonder why?
Atto even more in the $1200 range.
3 ware $1269
i wouldnt touch adaptec at this point..
so thats $480 more for a 8 port controller that does raid 3
now in all fairness we have not benchmarked a SATA 600 Areca. last tests we did were with an Areca sata 300 (still have it here)
vs other sata 300 cards. (Intel, 3Ware, Atto)
but when we did the $480 gained you nothing..
guess we have to run some benchmarks again.
Please post if you guys ever get that done. I'd be interested.