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RAID Question on TH7II-RAID

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Eggroll

Registered
Joined
Apr 5, 2002
If I want to set-up a RAID 1 (mirror) with two drives, is it better to put them both on IDE3 as master and slave or to put them as individual masters on IDE3 and IDE4? It doesn't seem to specify in the manual the best way to do it, at least that I could find.

I'm guessing I can do it either way, but I'm wondering if I set them both up on IDE3, if that will enable me to add more drives at a later date to expand the array as an even larger drive, perhaps a RAID 0+1 or just a bigger RAID 1, without losing all of my data.

Any suggestions would be greatly appreciated.

Thanks,
Eggroll :)
 

donny_paycheck

Inactive Super Quad Mod
Joined
Oct 25, 2001
I have a KR7A-RAID but it has the HPT372 chip on it. For a RAID 0 obviously seperate channels are better. For RAID 1 it might not seem like it would be, but it is.

The reason you will still get better performance by splitting the drives across the channels is because, even though it's a mirror, the RAID chip isn't sending the identical data to each drive right down to the microsecond. Say, it sends 010101110101 to device 0, then it'll send the same thing to device 1 only millisecond later. Not at the exact same time. The chip will have to send the bit stream to each drive indipendently and having the channel clogged with the same bit sequence for the other drive will make it wait and then resend it. With each one on its own it can do both at once and not worry about contention.

For this reason you want to give each drive its own channel because crowding them onto the same ATA bus will give you a lot of bus contention, which will slow things down tremendously.

Split them up.
 
OP
E

Eggroll

Registered
Joined
Apr 5, 2002
Thanks, dp. That makes sense. Ignoring the performance hit for the moment, though, is one approach going to be better than the other for adding drives at a later time? That is, will one way allow me to simply add the drives in and expand the array with the RAID admin without starting over from scratch? Or will it be the same advantage or problem either way I do it?

Thanks again for the fast response.

Eggroll :)
 

donny_paycheck

Inactive Super Quad Mod
Joined
Oct 25, 2001
Eggroll said:
Thanks, dp. That makes sense. Ignoring the performance hit for the moment, though, is one approach going to be better than the other for adding drives at a later time? That is, will one way allow me to simply add the drives in and expand the array with the RAID admin without starting over from scratch? Or will it be the same advantage or problem either way I do it?

Thanks again for the fast response.

Eggroll :)

What exactly do you want your upgrade path to be?

If you had both drives as a RAID 1 on IDE3, then you'd still have to start over from scratch when going to 0+1 and adding another pair of drives to IDE4. Really any way you cut it you're going to be redoing everything if you add drives to the array. Onboard ATA RAID chips like the Highpoint are pretty rudimentary devices and don't have a lot of flexiblity features like server SCSI RAID adapters.
 
OP
E

Eggroll

Registered
Joined
Apr 5, 2002
donny_paycheck said:

What exactly do you want your upgrade path to be?

Either doubling my size and keeping it RAID 1 or doubling my size and making it a RAID 0+1. You answered the RAID 0+1 thing, so I guess my remaining curiosity is if I kept it as RAID 1, is there an advantage to either approach?

Thanks,
Eggroll :)
 

donny_paycheck

Inactive Super Quad Mod
Joined
Oct 25, 2001
If you kept it RAID 1 then yes, you could just add drives to IDE4 and then mirror them from the drives you already had. With this you'd have a 3-4 drive RAID 1 with just the capacity of a single drive. A lot of redundancy but inefficient with space. Just thought I'd point that out in case you forgot or something.
 
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Eggroll

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Apr 5, 2002
Okay, I just realized what wasn't registering in my brain. I can't double my storage capacity by adding two more drives without striping. If I have two 60GB drives now and one mirrors the other, then I have 60GB of storage to work with. If I add two more 60GB drives, I can't get 120GB of available mirrored storage in a single array without also striping. I simply end up with more redundancy of the original 60GB drive. Right? In order to get 120GB of mirrored storage out of four 60GB drives it would have to be RAID 0+1. Even though it's a basic idea, I wasn't seeing it.

At the risk of beating a dead horse, this leads me to one more question. Is the RAID controller able to control more than one array? Say perhaps one on each IDE channel? I'm not talking about one big array partitioned into separate volumes. I mean a 60GB mirrored array on IDE3 (2 drives as master and slave) and a 60GB mirrored array on IDE4 (2 additional drives as master and slave.) Or, as an alternate, the first array with the drives as masters on IDE3 and IDE4 and the second array with the drives as slaves on IDE3 and IDE4. This second approach seems like it would be ideal because, no matter which of the two arrays you were writing to, you would be pushing data through separate IDE channels, maximizing throughput performance.

Sorry if this is starting to drive you crazy. I'm just trying to figure out all of my options so I can make the best choice and only do it once.

Thanks again for all of your help.

Eggroll :)
 

donny_paycheck

Inactive Super Quad Mod
Joined
Oct 25, 2001
Yes, that would work. You could have two 120GB RAID 0s with the masters on IDE3 and the slaves for each on IDE4 without affecting performance. The RAID chip is capable of that. I wouldn't put the master and slave of each stripe on the same channel because then you'd have the bus contention issue that you'd have with a RAID 1 on IDE3 or similar.