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Old 08-14-2008, 04:26 PM   #1
durino13
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SATA controllers and RAID - the basics


Dears,

I want to upgrade disk space on my home server and I have bunch of questions. I've read tons of stuff, but I think, I still miss the basics, so I better ask in advance.

1.
I need a SATA (PCI) controller with RAID support. I understand, I have 2 options (HW,SW). I want to go for SW. HW is expensive and also if the HW controller fails, I won't be able to recover without having the same type of controller, correct?

2.
My biggest concern is follows: As I understand, there are 3 types of controllers.

a. HARDWARE (REAL) SATA CONTROLLER --> $$. CPU is offloaded.
b. HARDWARE (FAKE) SATA CONTROLLER --> e.g.: http://www.highpoint-tech.com/USA/rr1640.htm. Most of the RAID stuff is handled by CPU.
c. 'NORMAL' SATA CONTROLLER --> some SATA controllers *DO NOT* advertise with RAID capabilities, however they have 2 or more SATA ports. Can I build SW RAID above them?

(From: http://linuxmafia.com/faq/Hardware/sata.html) "You're advised to blow away fakerai volumes, use SATA drives as straight block devices, and enable Linux software RAID instead, during Linux installation."

Does this mean, that I don't need any special RAID enabled card and I can do all using linux 'md' drivers?

3.
Will a PCI card be a bottleneck? What about CPU load while running SW raid?

4.
The HighPoint card says, it has driver support for RedHat, Suse .. But I have a debian etch (2.6.18 kernel) box. Could this be a problem?

5.
Could you give me a general hint, how to proceed? I mean, I definitelly need to buy a peace of hardware, because I don't have SATA support on my MB. My biggest concern is, what controller should I buy.

Thx for help in advance.

Juraj
 
Old 08-14-2008, 04:47 PM   #2
CRC123
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1. Correct, most of the time when you buy a raid card that is based at in hardware, you have to have that same hardware (or older/newer version of it) for recovery.

2. Software raid in linux will work on ANYTHING. You can mix and match ide, sata, and external drives if you like! Though I would always try to use the same interface if possible. Also, software raid deals with individual partitions instead of whole drives, so you can have part of a drive be in a raid array and the other be a regular ext3 partion.

3. Interesting point; anything having to do with computing a parity bit or data, will be a performance hit (even on fakeRAID) by default.

The PCI bus specs say there is a max transfer rate of 133MB/s. I would say that most sata drives can sustain around 50-60MB/s of SEQUENTIAL access throughput. Absolute worst case, RAID0 would have two disks doing this simultaneously for a throughput of around 100-120MB/s of data. If you only have those drives on the bus, that's fine, but the reality of it is that many things use this bus (cd, network, etc).

So, worst case there would be a bottleneck, but for standard use I don't think it would amount to much, so I wouldn't worry about it.

4. Possibly, when they say that only those distro's are supported, they mean that those distro's are the only ones they tested with the card. It may work on yours.

5. Newegg generally has good prices and reviews. You can spend under $50 and get a SATA controller that will be fine for software RAID1 and RAID0.

Good luck
 
Old 08-15-2008, 02:38 AM   #3
durino13
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Registered: Jul 2008
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Quote:
Software raid in linux will work on ANYTHING
I will not spend to much money in controller then. I will make sure, that my SATA drives are working and I'll leave the RAID stuff to be handled by the kernel.

You have helped me a lot!! Thank you.
 
  


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