8x 1.5tb on LSI MegaRAID = very slow

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bazaarboy

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Nov 18, 2009
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Hi any help is appreciated:
8x Samsung Spinpoint F3 1.5TB
on
LSI MegaRAID SAS 8208ELP
RAID5

Real world rrite speeds about 10mb/sec! and reads about 60mb/sec

HD Tune shows a different picture:

cb4c4cd9e9.jpg


can anyone tell me why write speed are so slow?? thanks
 
the array sits as drive E on a vista64 machine (using a 7200rpm RAID0 C drive)
if I copy a large file from C to E, it transfers at about 10-12mb/sec
if I copy from E to C the speed is more like 60mb/sec!
 
What's the complete setup hardware wise? CPU, RAM, Motherboard, OS, etc... Also are you using the latest LSI driver for the controller and have the latest firmware loaded onto the controller.

How much RAM does the LSI controller have and what is the internal cache setup? Also does the controller have a battery backup unit attached, and is write caching turned on?

RAID5 will typically have slow write speeds due to parity calculations if the RAID controller has a slow CPU (or no dedicated XOR CPU), and/or it's cache profile setup is not geared for RAID5.

I would (based on the info given):
1. Check that the cached writes is turned ON in the controllers BIOS.
2. See if you set the percentage of cache more geared for writes than reads. (Some BIOSes don't have this option). It's been a while since I've used LSI controllers.
3. Switch to RAID 10, and see if this improves your overall performance.
4. Update to Windows 7...
 
Hi thanks for your comment - the machine is a core-duo (E6600) with an ASUS P5W Deluxe motherboard. It uses two WD drives (7200rpm) in Raid0 on the onboard controller for C drive...
I will check if the cached writes are on
I would rather not switch to raid10 as the array already has about 5.6tb of data
windows 7 sounds tempting
 
That's an "entry level" RAID controller according to LSI's marketing materials. It's entirely possible that with eight drives in a RAID5 configuration, you're just swamping whatever onboard CPU that thing has.

I'd suggest trying a softraid5, but it doesn't sound like you're on a platform that offers it.
 
Can you check the SMART data for each drive and look for high levels of CRC related errors or any sector remappings (basically anything that might look bad in the SMART data)? Are the drives directly connected to the RAID controller, or are you using some kind of bay?

Is this array being used with live data right now? Can you play around with configurations to determine issues? For example, can you try 3 drives in RAID 5 and rerun performance tests. That could help to confirm or deny the claim Mercutio suggested about you overloading the controller. If the speed increases dramatically, then it's possible the controller is overloaded, or that maybe one of the drives is bad, or a cable/connection is bad. Then you can try swapping cables and retest to eliminate cables. Next, try again as a 3-volume RAID 5 using 3 different drives.
 
Something better than half your HD tune results. Or were we swapping bits and bytes around somewhere?
 
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