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RAID and storage limits

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March 25, 2010 11:49:06 PM

Ok, so I'm new to the whole RAID scene but am looking into building a RAID 5 setup for NAS or a server. I'm also trying to do this as cheap as possible as I am also buying a new laptop this summer. I've been scouring the internet and have stumbled upon this product:

http://www.addonics.com/products/host_controller/ad5sah...


From what I can read that will allow me to connect up to 5 drives, set them up in a RAID array, and then output them through eSATA to my computer. Now the big question is it mentions a 2TB limit for 32bit OS's, but tons more for 64 bit. I've got an old tower at home I was planning on connecting this to running good ol XP. Does this mean that using this device to connect it up to my XP tower would limit the entire RAID array to 2TB of total storage? I was planning on using 3+ 1TB drives, and it being older hardware I don't think I can run a 64 bit OS on the tower.

Any help would be appreciated!

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a c 415 G Storage
March 26, 2010 12:12:05 AM

The traditional "MBR" (Master Boot Record) partition table can only handle drives up to 2TB. To create partitions beyond the 2TB limit, you need to use a GPT (GUID Partition Table).

Windows 7 and I believe Vista support GPT partitions, but AFAIK XP does not.

Windows 7 will happily work with GPT partitions larger than 2TB on ANY drive, including the boot drive.

BUT - the BIOS in most motherboards can only boot from MBR partitions. To boot from a GPT partition, you need a BIOS that supports EFI (Extensible Firmware Interface). Desktop motherboards support this are still rare.

You have to ask yourself what you're expecting from RAID 5. RAID 5 is not a good choice for very large arrays because the expected unrecoverable error rates on hard drives (typically 1 unrecoverable read error per 10^14 or more bits read) mean that there's a fairly good chance that you won't be able to recover from a drive failure. RAID 6 (which uses two parity drives) is a much safer choice, but is not supported by a lot of RAID controllers.

If you're looking for data protection, you'd be better advised to put some of these drives in external enclosures and use them for backups.
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March 26, 2010 12:46:01 AM

So once the computer's already into the OS than it should read all the space, correct? I won't be booting from this array, but just store all my media and such on it.

I've got a fairly large collection of movies and such that takes up over 1 TB and will probably get up to 2. I don't want 1:1 backups of it all cause that's such a waste of drive space that I wouldn't be too hurt over if I lost it. RAID 5 just looked appealing since I wouldn't need to dedicate that much drive space to have at least a little piece of mind. And if my data collection grew bigger i would just do 2 or 3 smaller RAIDs than 1 large one.
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a c 415 G Storage
March 26, 2010 12:51:07 AM

Yep, if you boot from another drive and use Windows 7 or Vista then you won't have any problems with a volume over 2TB.
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