More RAID Questions

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More RAID Questions

Postby pk_fox » Mon Mar 31, 2014 6:26 am

Hi all, I have a HP Proliant ML330 which has a P401 raid controller, at present it is fitted with two dual port 300 gb SAS drives, my question is can I add two more drives and set them up as a separate logical drive ? Unfortunately the server has Windows on it at the moment but will be running Fedora eventually when I have time to copy the data off. I was thinking of a pair of 1 tb SAS drives configured as RAID 1
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Postby johnhudson » Mon Mar 31, 2014 9:06 pm

What you have is fake raid. If you install Linux, you would be far better using mdadm. Some distros will set it up for you.

The main point is that, whatever RAID you use, you need matching drives.
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Postby pk_fox » Tue Apr 01, 2014 5:31 am

johnhudson wrote:What you have is fake raid. If you install Linux, you would be far better using mdadm. Some distros will set it up for you.

The main point is that, whatever RAID you use, you need matching drives.


Hi there and thanks for answering, what do you mean by matching ?, matching as in capacity, or drive model, or serial numbers ? , single or dual port ?
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Postby nelz » Tue Apr 01, 2014 7:29 am

Matching in capacity and performance parameters (speed, cache size etc). It isn't strictly necessary, Linux software raid can cope with different sized drives, it ignores the extra space on the larger drives, but for best performance they should match.

They don't need to be fro the same manufacturer, in fact there is a school of thought that says they should be from different manufacturers. From time to time, any manufacturer can produce a batch with a higher failure rate, you don't want a RAID full of these, mixing makes can reduce the chance of multiple drive failures.
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Postby pk_fox » Tue Apr 01, 2014 11:06 am

nelz wrote:Matching in capacity and performance parameters (speed, cache size etc). It isn't strictly necessary, Linux software raid can cope with different sized drives, it ignores the extra space on the larger drives, but for best performance they should match.

They don't need to be fro the same manufacturer, in fact there is a school of thought that says they should be from different manufacturers. From time to time, any manufacturer can produce a batch with a higher failure rate, you don't want a RAID full of these, mixing makes can reduce the chance of multiple drive failures.


Ok thanks, but that raises another question ? does software RAID do away with the need for a hardware RAID controller ?
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Postby nelz » Tue Apr 01, 2014 11:12 am

Yes it does. If you have a proper hardware RAID controller you can use that, but if it is fakeraid steer well clear.
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Postby pk_fox » Tue Apr 01, 2014 11:25 am

nelz wrote:Yes it does. If you have a proper hardware RAID controller you can use that, but if it is fakeraid steer well clear.


How do I know if it's fakeraid ?
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Postby nelz » Tue Apr 01, 2014 11:33 am

Google the RAID controller details. Or you could try booting from a Linux live CD, if the pair of drives show up as a single devices, and it is not /dev/md0, you have hardware raid. FakeRAID is basically software RAID using a Windows driver.
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