Strange RAID5 HD Tach Reading

[Captain Fizz]

Hello folks,

I have 3 x Seagate Barracuda 7200.9 250GB ST3250824AS SATA-II 8MB Cache.

I put them in a RAID5 array on the nVidia controller on my Asus A8N32-SLi.

But the results have large areas of slow speeds...

Any ideas?

After reading more reviews...
Am I worth going for RAID5 on the nVidia's built in controller?
(Write speeds seem alarmingly slow)

 

[earlyflash]

That does seem odd. Can you check the health of the driveS? It may be that one of the drives is offline in the RAID5 set, since it would be rebuilding the data from parity, that would explain the notchyness of the reading.

On my RAID-5 array (Promise internal PCI card, not Nvidia) it's 100MB+ all the way across the array, although mine is a 4 drive array.

 

[rpstewart]

Am I worth going for RAID5 on the nVidia's built in controller?
(Write speeds seem alarmingly slow)

In a word, no. The nVidia RAID has no hardware XOR engine to do the parity calculations so it has to hand all that off to the CPU which a) slows the rest of the system down and b) slows disk writes.

Out of interest I get a similar shape of graph from my RAID5 array (8*250 on RocketRaid 2320) but no where near as big a difference between the peaks and troughs (20Mb/s or so) and a more sine wave shape. I'm guessing it's to do with two of the drives in the array only running at ATA100 rather than SATA150

 

[Captain Fizz]

I will check them when I get home.

One was a new drive, the other two I had copied data off of just before creating the array.
(the new drive showed up no problem in Disk Mgmt)

EDIT - Also, all the drives are definitely SATAII 300MB/s.


EDIT2 - Will break the array again tonight.
Test each drive individually again.
They WERE all working. ??

If I manage to get the 3 working as normal, then will be adding a 4th.
Not too worried about write speed, data retrieval is what this will be getting used for.

EDIT3 - - Ordered 4th drive.
Will break the array tonight and test each drive individually.
And the 4th when it arrives.
Will try again then.

 

[Captain Fizz]

Right - An update for those that posted here...

Tried several other benching proggies, and the all important "Actually using it" test.

Seems like it is actually over 100 meg all the time.

\o/

Write speeds are poor, dire in fact!
But I have another drive on it's way to work with files etc.

The read speed of the array is perfect though - And for it's job (file server, mainly other people accessing it so read speeds more important) it's spot on.

So keeping the array as it is.
Cheers for th ideas though.

 

[Dunky]

Write speeds are poor, dire in fact!

That is one of the tradeoffs with RAID 5, especially with software XOR engine. The low write speeds are usually attributes to the generation of the parity bit used to recover data if a drive goes offline. It's worst when your CPU is under load and although a hardware RAID 5 controller takes the strain off the CPU, write speeds are still not too great.

But for a file server it's great and the read speed makes up for the lack of a decent write speed.