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Large RAID Setup, Slow Transfer Speed

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  • NAS / RAID
  • Enclosure
  • Storage
  • Product
Last response: in Storage
September 21, 2011 1:53:58 AM

I setup a raid system with Cavalry 4 bay enclosure through esata card, which promises 3Gbit/s speed, or 384MB/s equivalent. I have 4 2TB 5400 Hitachi drives setup with RAID 5 running on Win 7 64bit. But my transfer speed is super slow! I tried moving files over, for the first 2-3 seconds or so, it would race at 150-175mb/s, but then it slows to a crawl at around 4-6mb/s. This is unacceptable. I'm not sure what is wrong, and admittedly I'm a noob at this.

Appreciate any help!

More about : large raid setup slow transfer speed

a b G Storage
September 21, 2011 2:49:41 AM

Thats becasue of the mechanical bottleneck, you can speed things a little bit by making it RAID 0. Sell one of the drives and get a external drive for backup, RAID5 sucks nowadays in terms of data security
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September 21, 2011 2:54:39 AM

Thanks for your quick response...can you elaborate on what exactly do you mean by "mechanical bottleneck"? Raid 0 does not have the redundancy I need. Is all raid 5 setup through external interface (esata) this slow? I find it hard to believe that 4-6mb is the best transfer speed I can get.
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a b G Storage
September 21, 2011 3:30:34 AM

mechanical bottle neck? thats one hell of a bottle neck... sequential read speeds should maintain rather high. unless you are transferring thousands of 30kb files you should be well over 100MB/s. ensure the raid is not damaged and is properly functioning. your raid control software should tell you this. do not make this a raid-0, raid-0 should only be used where data is not important and regular backups should still be maintained. raid5 is the correct raid to use in this situation.
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a b G Storage
September 21, 2011 2:50:16 PM

leandrodafontoura said:
Thats becasue of the mechanical bottleneck, you can speed things a little bit by making it RAID 0. Sell one of the drives and get a external drive for backup, RAID5 sucks nowadays in terms of data security




Mechanical bottleneck? RAID 5 sucks in terms of data security? Then you recommend RAID 0 (which has no reduncancy) as an alternative? You, my friend, need to go read up on RAID arrays. You obviously know absolutely nothing. We use RAID5 on our Exchange servers, as well as all of our file servers at work. It provides great redundancy, and when implemented properly, provides good speed. We use Dell MD1000 disk arrays (with 15 x 1TB drives in each one) on a Dell PERC RAID card. I run them as split RAID5 arrays, with a global hot spare. They can sustain 80-90MB/sec in that configuration on each array. Mechanical bottleneck my ass. It's called improper implementation.


To the original question -

It's a matter of using a poor quality controller. Those low-price external enclosures usually use bare-bones RAID controllers that have slow parity engines, and lack the required cache on-board to properly handle RAID5. While a lot of them advertise RAID 0/1/5/10/JBOD, they typically only run 0/1/10/JBOD very well. RAID5 requires calculations be performed to generate the parity data. For serving up large files / movies, you should run a 128k strip size, but i'm willing to bet that enclosure doesn't let you configure that.


RAID5 is a great solution for when you need maximum space, good redundancy, and average to good speed.
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September 21, 2011 4:58:03 PM

mavroxur said:

It's a matter of using a poor quality controller. Those low-price external enclosures usually use bare-bones RAID controllers that have slow parity engines, and lack the required cache on-board to properly handle RAID5. While a lot of them advertise RAID 0/1/5/10/JBOD, they typically only run 0/1/10/JBOD very well. RAID5 requires calculations be performed to generate the parity data. For serving up large files / movies, you should run a 128k strip size, but i'm willing to bet that enclosure doesn't let you configure that.


RAID5 is a great solution for when you need maximum space, good redundancy, and average to good speed.


Thanks for answering. The raid software manager actually does let me configure the "chunk size", which I did some research and it is the strip size, which I have set to 128kb as you mentioned knowing I am moving large files. I guess I'm going to have to call them up for customer support. By the way, the manuals and instructions for this product is absolutely TERRIBLE!!! Cavalry does a bad job.
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a b G Storage
September 21, 2011 6:44:16 PM

raid123 said:
Thanks for answering. The raid software manager actually does let me configure the "chunk size", which I did some research and it is the strip size, which I have set to 128kb as you mentioned knowing I am moving large files. I guess I'm going to have to call them up for customer support. By the way, the manuals and instructions for this product is absolutely TERRIBLE!!! Cavalry does a bad job.






I've seen several external RAID enclosures over the years, and unfortunately, most of them are terrible. (at both RAID5, and the documentation/support). The only way i'd ever do an external RAID5 is with eSATA/SAS to an internal controller. The weak IOP's that the external RAID enclosure makers generally use, combined with no cache, makes them suitable for non-parity RAID levels only IMO.
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a b G Storage
September 21, 2011 6:45:12 PM

listen to mavroxur, not leandrodafontoura.

i concur, the problem likely has something to do with that enclosure not being able to handle parity calculations well.
if you get a proper hardware accelerated raid controller card you would see 150-200MB/s (both ways).
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a b G Storage
September 21, 2011 8:41:12 PM

good answers, i myself have not used any off the shelf nas storage systems but i do use a linux box with a acrea raid card in it with 3 drives for my nas. i easily get 250MB/s off that.
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September 28, 2011 12:12:39 AM

Best answer selected by raid123.
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