HD Speed

rowdy · 03-08-2005, 11:24 PM

Hi,
I have two 80Gig IDE HDs in raid 0 config. I also have 120Gig SATA drive.
I have speed tested these drives and my SATA drive gives 57 MB/sec and my raid config only gives 55 MB/sec.
I used HDspeed.
Why is my raid config slower than my SATA?
I thought raid would double my speed.

crazijoe · 03-09-2005, 06:29 AM

There is a lot of factors in this. First, you must look at all the specs of the drives and not just the advertised transfer speed. A typical IDE drive transfer speed is 100MB/sec or 133MB/sec and a SATA advertise transfer speed is 150MB/sec. Now lets dig in and look at the actual transfer rates. We'll use Seagate for an example.
IDE
http://www.seagate.com/cda/products/...85,581,00.html
SATA
http://www.seagate.com/cda/products/...85,587,00.html
If you look a the Max External speed, that is where you will see the advertised speed. But if you look at Avg. sustained speed, this would be more practical. The Interface (where you connect the cbales to can transfer at 133MB/s max but the head to disk (internal) can only transfer about 50 to 60MB/s. This would hold pretty much true to all hard disks, SATA, IDE, SCSI, etc..
Now lets look at another factor. The PCI bus. If you have a controller that is connected to a PCI slot or is integrated to the MB, chances are they are running off the PCI BUS. The PCI bus has a max throughput of 133MB/s. If you have a RAID 0 array of 2 drives, you have almost saturated it. If your SATA controller is not part of the south bridge chipset, you just added more components to the PCI bus. Now, also take into concideration that your sound, LAN, etc. are also connected to the PCI bus, you will eventually exceed the bandwidth of the bus.
The first thing I would do is check the HD manufacturers specs and see what the avg. sustained transfer rate is of the IDE drives.
I have 4 WD Raptors in a RAID 0 array and my average transfer speed is 119MB/s. I'd like to get more but this isn't going to happen on a 32 bit PCI bus. (especially with having GBe LAN also)

rowdy · 03-09-2005, 08:27 PM

Thanks for your response.

Disk to buffer transfer rate is 525 Mbits/sec.
Buffer to host is 100 MBytes/sec
No data available for sustained rate.
The max rate I am getting is 63 Mbytes/sec.
This is what I would expect from a single drive so why do I not get a higher rate from two drives on raid?
My SATA drive is getting 110 Mbytes/sec so the PCI bus is not the problem?
I have both drives on the one cable. Should I put them on separate cables?
Thanks

crazijoe · 03-09-2005, 09:36 PM

Quote:

Originally Posted by rowdy

I have both drives on the one cable. Should I put them on separate cables?
Thanks

Yes,
Both drives are sharing the bandwidth of the single cable. Not very efficient.
Put each drive on separate IDE channels of the RAID controller.

03-08-2005, 11:24 PM	#1 (permalink)
rowdy Registered User Join Date: Mar 2005 Posts: 2 OS: xp	HD Speed Hi, I have two 80Gig IDE HDs in raid 0 config. I also have 120Gig SATA drive. I have speed tested these drives and my SATA drive gives 57 MB/sec and my raid config only gives 55 MB/sec. I used HDspeed. Why is my raid config slower than my SATA? I thought raid would double my speed.

03-09-2005, 06:29 AM	#2 (permalink)
crazijoe Registered User Join Date: Oct 2004 Location: Omaha, The Center of the Universe Posts: 7,632 OS: WinXP, Win2K3 My System	There is a lot of factors in this. First, you must look at all the specs of the drives and not just the advertised transfer speed. A typical IDE drive transfer speed is 100MB/sec or 133MB/sec and a SATA advertise transfer speed is 150MB/sec. Now lets dig in and look at the actual transfer rates. We'll use Seagate for an example. IDE http://www.seagate.com/cda/products/...85,581,00.html SATA http://www.seagate.com/cda/products/...85,587,00.html If you look a the Max External speed, that is where you will see the advertised speed. But if you look at Avg. sustained speed, this would be more practical. The Interface (where you connect the cbales to can transfer at 133MB/s max but the head to disk (internal) can only transfer about 50 to 60MB/s. This would hold pretty much true to all hard disks, SATA, IDE, SCSI, etc.. Now lets look at another factor. The PCI bus. If you have a controller that is connected to a PCI slot or is integrated to the MB, chances are they are running off the PCI BUS. The PCI bus has a max throughput of 133MB/s. If you have a RAID 0 array of 2 drives, you have almost saturated it. If your SATA controller is not part of the south bridge chipset, you just added more components to the PCI bus. Now, also take into concideration that your sound, LAN, etc. are also connected to the PCI bus, you will eventually exceed the bandwidth of the bus. The first thing I would do is check the HD manufacturers specs and see what the avg. sustained transfer rate is of the IDE drives. I have 4 WD Raptors in a RAID 0 array and my average transfer speed is 119MB/s. I'd like to get more but this isn't going to happen on a 32 bit PCI bus. (especially with having GBe LAN also) __________________ Microsoft MCSA + Messaging, MVP, A+, Network+ http://i16.photobucket.com/albums/b3...other/Help.jpg Do you want a real Republican? HDD diagnostic tools / HDD data recovery software

03-09-2005, 08:27 PM	#3 (permalink)
rowdy Registered User Join Date: Mar 2005 Posts: 2 OS: xp	Thanks for your response. Disk to buffer transfer rate is 525 Mbits/sec. Buffer to host is 100 MBytes/sec No data available for sustained rate. The max rate I am getting is 63 Mbytes/sec. This is what I would expect from a single drive so why do I not get a higher rate from two drives on raid? My SATA drive is getting 110 Mbytes/sec so the PCI bus is not the problem? I have both drives on the one cable. Should I put them on separate cables? Thanks