raid 5 write speed decreasing

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hongabonga

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Jul 2, 2014
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hello guys I have a raid 5 with 3 * 1 TB 2 western digital green and 1 black at the beginning write speed was 50 mb/s after initializing 10 mb/s now 4 mb/s the cpu quad 2.8 ghz gigabyte mb intel controller 8 gb ram I had enabled the write cach back where is the wrong with it?????????
 
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drtweak
Unless you have a UPS on that system or it has a nice RAID Card with a BBU don't enable write back cashe. Enable it as just Write Throught. You will lose data if you have a power outage and its doing stuff.

Also you're mixing Green and Black drives. Green drives are NOT recommened for RAID because they vary in RPM and also turn them self off after a while and can cause issues with the RAID depending on how long the timeout period is on the RAID Controller.
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drtweak

drtweak

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Sep 17, 2012
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Unless you have a UPS on that system or it has a nice RAID Card with a BBU don't enable write back cashe. Enable it as just Write Throught. You will lose data if you have a power outage and its doing stuff.

Also you're mixing Green and Black drives. Green drives are NOT recommened for RAID because they vary in RPM and also turn them self off after a while and can cause issues with the RAID depending on how long the timeout period is on the RAID Controller.
 
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drtweak

drtweak

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Well Green drives with RAID in general aren't all that great because of their tendnacy to turn off and variable RPM. In a RAID is BEST to at least have them all the same RPM Speed all the time. You could try a Raid 1 with the Green drives. At least this way They are both accessed at the same time so its not like one will timeout before the other or cause any issues. But for anything more than a RAID 1 i wouldn't recommend green drives or any drive with a variable RPM in a Raid to begin with. Mixing RPM's like a 5400 and 7200 aren't as huge of a deal but its always best to have the same drives in each arrary
 
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FireWire2

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Depend on your SATA RAID Engine - note: Not every RAID are the same!.
But mainly when you use Motherboard's RAID engine you are:
- Using Software RAID
- Your system is likely bombarded with IRQ from those HDD, and your CPU run out of time (not power)
to test it, do this:
Copy/Paste a file to itself, look at the CPU Usage in Windows Task Manager. If the transfer is under 50MB/s (big B) and CPU goes about 10%~20%.

A new RAID engine is recommend. get one of these RAID card:
http://www.newegg.com/Product/Product.aspx?Item=N82E16816103229&cm_re=RAID_card-_-16-103-229-_-Product
or
http://www.amazon.com/multiplier-hardware-RAID0-CLONE-Controller/dp/B004JPUZWU

Then you will have over 200MB/s read/write.
 
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hongabonga

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THANX FIREWIRE I TRY THE TEST IT GIVES ME 10% cpu suage for 2 seconds then 0% usage I use intel raid controller built in with motherboard but I would like to understand your word (Your system is likely bombarded with IRQ from those HDD, and your CPU run out of time (not power) ) do you mean that is the resources is not enough ?
 
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FireWire2

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This is a classic issue when use Motherboard RAID

Each of HDD drive when read/write, it has to send numerous of IRQ to CPU to get a command instructions. It's in a range of 1000's times per second, although this IRQ does not cost CPU power, matter of fact it takes every little, but it costs CPU timing... Now multiply it with number of HDD that you have. The CPU is being bugged for 10K's of time per second easily

Note: i just paint a simple picture for you to see, it's lot more complicate then what i state here.

Just like this scenario:

Let say you are very efficient on your work (CPU) but under you have 5x workers (HDD) that every move, each worker has to ask you (CPU) instruction of how, you productivity will goes down because you do not have time to do anything else.

This is why all high end systems have hardware RAID :)

 
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hongabonga

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Jul 2, 2014
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thanx again firewire I had understand it finally I will buy a raid controller and change green drives in my array but in case of emergency when raid controller damaged I think that I must buy the same or it will not be work iam right ????
 
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drtweak

drtweak

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The way RAID works and the Reason why it erases all the data on the drives is because it write the RAID info to the Hard drives as well. For the most part you SHOULD be able to transfer it to any other SATA controller and it should see that there was a RAID there and you can import the config into you new RAID Controller.

Now I HAVE done this but only from one Dell PERC RAID Card to another (They were different RAID Cards two. One was a Dell SAS 5 controller to a Dell PERC H310. The thing is they all use LSI chip's. I've been meaning to take a RAID from an Intel or AMD Chipset and try to import it over.
 
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FireWire2

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If the RAID is damaged, the easiest way is replace the same controller or same manufacture RAID controller, most of the time it has the same RAID engine...
Or use Linux mdadm to read the data of those HDD, because it's a conventional RAID.

BTW the RAID card damage is very unlikely, unless you spill, zap or put is next to Video Card heat sink (hot environment)

 
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