Raid5 write performance

[Guest]

Hi all, hope you can give me a pointer of some sort

Motherboard: p6t deluxe
CPU: Core i 7 920
Ram: 6x1gb @ 1600mhz

I've got these disks: (detailed conf: http://www.intertech.dk/Rapport.txt )
1 stk. Intel 80gb SSD 1. gen
3x1gb WD Green 5400rpm i RAID5
1x1gb WD green 5400rpm
Alle disks on the same controller (IntelICH10)

My issue is that i experience a way too low write performance, both in these CrystalDiskmark tests and IRL
Scrn. shot of Crystal diskmark tests.
SSD http://www.intertech.dk/SSD.jpg
Single WD green - http://www.intertech.dk/SingleDisk.jpg
3xWD Green i Raid5 - http://www.intertech.dk/Raid5.jpg

Any advice are taken

Of, one thing.... it sounds like the disks are working all the time.. are raid5 disks supposed to do that (building parity ex.?)
Swap file on the single WD green

*hoping

 

[Guest]

Tried configuring the drives for Raid0, and NO performance issues there: http://www.intertech.dk/Raid0.jpg so the disks are fine

 

[HappyBison]

This is normal and this is how RAID5 works. It works fast on read, but slow on small writes:
http://en.wikipedia.org/wiki/Raid-5#RAID_5_performance

 

[sub mesa]

You can enable 'write caching' option in the Intel ICHxR RAID drivers (unless you use Software RAID on Windows) to enhance performacne. Especially the sequential RAID5 write speeds would be alot higher. It does come at a certain risk though, of corruption in case of a crash or power outage. But with this kind of fragile RAID setups you need a backup anyway; don't think RAID5 will protect your data sufficiently alone.

But you should be able to get about 80MB/s sequential write with the Intel drives, using RAID5.

 

[HappyBison]

Just to add...
Write caching is a nice feature, but if anything could go wrong with the power, then you may lose your data really easy.
That's why many RAID5 controllers has a battery-backed up memory on it so it will save the data when power was lost.

If you can stand for your power (i.e, you have good UPS), then you can try to enable write cache. Otherwise I would not recommend it for important data.

 

[spoofedpacket]

Happy, just adding to what you started..

The issues with non-battery backed cache cut so deep into reliability that any 'real' RAID controller will only allow RAID0 and RAID1 on their controller unless it detects a battery backup on the card. A fine example is the Hp line of RAID controllers.

As for using a UPS, this sounds fine and dandy, but that does not save you if your OS crashes/freezes or your SATA drivers freak out. Controllers with a battery backed write cache have their own CPU and will save continue to flush cache after the system experiences a critical error. If something happens to the system where it can not flush the cache before a reset, it will flush the data the next time the system comes online.

My advice: Get a fourth drive and do RAID0+1. Two mirrored stripes. It is very simple for the system to manage, so your onboard controller won't be offloading much work on the CPU and allows you to lose two drives and still keep on truckin. You would also get a pretty massive read speed and writes would be just fine.

 

[Guest]

Thanks a LOT for all your help. I've got perfect answers to my questions. Though the enabling write cache seems to sovle my problem, i can't live with the risc factor.
I'm gonna go with the 2disk raid0 and then backup the important files on the third drive. Then some time in the future, get a real NAS thingie with at proper controller (with write cache)

Again, thanks! for the answers, they where really usefull.

 

[Telek]

If you have ICH10R then use MatrixRaid and setup 2 partitions - one as RAID0 across 2 disks with 1/2 the space, the other as RAID0/1 across the same 2 with the 3rd as the mirror. That way you don't have to do any manual backup, anything important just keep on the RAID0/1 partition.