redu GPT from non-efi motherboard

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ltokuno

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Sep 25, 2013
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Hello,

I have a 3tb drive that was partitioned and formatted on a system without EFI support. Now when I use it on a system with UEFI support the drive gives me about 5MB/s transfer rate. All this is under Win 7-64.

Is there some way of fixing a weird GPT on the drive without losing data? Or is there some way to tell windows that this drive is “special”, and go about using it the old way without native EFI support? I'm thinking no because of MB driver compatibility, but you never know.

The drive has about 1.8tb of data on it that I'd rather not lose.
 
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RealBeast

RealBeast

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Sep 13, 2010
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You only need EFI to boot from a GPT drive (>2.2TB). If it was formatted on an older system that used MBR you will need to backup the data, unpartition all existing partitions in disk management it and reformat using GPT on your modern Win 7 x64 system.

Check on the type of drive format by looking in disk management, right click on the small grey box area of the drive, select properties, click volumes tab and look at partition style -- it must say GUID Partition Table (GPT) to work properly.
 
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ltokuno

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Sep 25, 2013
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10,510



Well, it's already GPT. I don't think MBR will support a 3GB partition. It was partitioned and formatted with win 7 x64, only it was with an non-upgraded early version.

I did a little experiment, and booted linux live disk to check transfer rates. I was getting 100MB/s or more. So, I put in another drive and a fresh install of win7. Completely clean install. Ran a test transfer and still I get about 5MB/s. So I ran HD tune to check the drive speed and I get about 130MB/s. I'd rather not boot linux every time I want to transfer stuff to this drive. Any idea what in windows would make the transfer speeds crawl like that?
 
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ltokuno

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Sep 25, 2013
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I tested with a clean install of win7. No software installed. So there's no anti-virus to turn off.
 
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ltokuno

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Sep 25, 2013
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Update:
I know this is an old post, but I just found the answer to my problem. Turns out it was the cable. A friend of mine recently got a machine to test cables for his job. After a long conversation we decided to test out the sata cables in my machine. The new sata 3 cables I bought with my mother board turned out to be sata 2 cables and not rated for sata 3. This was also the case for my test cable which I thought was sata 3 as well.
The conclusion we came up with was that the bios read the disk and decided it was a sata 3 disk (it is) and tried shoving data at the drive at sata 3 speeds. The cable, not being able to handle sata 3 speeds threw out a bunch of errors, but between error correction and re-sends the data eventually went through at speeds of around 1-2MBps. When I found a cable that was up to sata 3 speeds (verified by the machine) the write throughput went to 80-90MBps which is fine for that setup.
I still don't know why it works with a faulty cable in linux, but at this point I don't really care.
 
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