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I just bought myself 2 x 3tb wd red drives and a startech 4 port raid card . Unfortunately, I have a very, very strong suspicion that this is a 'fake-raid' card as it is not from any of the main manufacturers like LSI or 3ware. Transferring files from a WD black 2TB to the raid 1 array is going at an appallingly slow rate of around 60MB/s. Would it not be faster to remove the card, and set up software raid with mdadm?

-- Update I just unplugged/unset the hardware raid 1 array, and re-plugged in the drives directly to the motherboard. Transfers direct from drive to drive appear to go at 120MB/s (exactly double). I realise that raid1 has to duplicate the data, but surely It reads at 120mb/s from one drive and each raid drive should write at nearly 120mb/s on each of the reds?

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2 Answers

up vote 3 down vote accepted

If you see the individual disks and the whole array shows up as /dev/mapper/something, then it's a fakeraid. While mdadm shouldn't be faster, it is better supported and recommended if you don't need to dual boot with windows.

It looks like this is some old hardware. It says it is legacy old PCI rather than any of the flavors of PCI Express. That means it is limited to a throughput of about 125 MB/s, and since you're writing the data twice to both disks, that's why you are only getting 60 MB/s.

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Good point about regular PCI bus! Didn't spot that one. I hope OP didn't pay that $67 for it... it should be $6 or less. –  gertvdijk Jan 8 '13 at 20:04
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To test if the performance goes up moving to mdadm using a proper host-bus adapter (AHCI) capable card, you should just try that out. I don't have this hardware available, but I can give you some general advice against using 'fakeraid' in favour of Software RAID:

  • Software RAID is totally independent on the controller you're using. In case the controller dies, you can just re-plug the disk in another one and access your data.

    (Okay, you may be screwed as your disks/data may die too after a controller failure, but that's another story.)

  • Software RAID has been tested more thoroughly. It's not just running on that particular device - the code is totally independent to it!
  • Easier recoverability. In case you totally screw up, more people will be able to help you out, as again, the format of the metadata on the array is independent of the controller.
  • Software RAID is more flexible. It allows you to change the RAID type (e.g. upgrade from RAID1 to RAID10, RAID5 to RAID6), resize the array, etc. Some of these features might come with the fakeraid card too, but it's not likely that all of them are included.
  • The driver for your fakeraid card may not be developed for anymore some later time. It could prevent you from upgrading the system/kernel. Software RAID is of course not affected by this.
  • In case you're troubleshooting performance issues, you're a lot more likely to get help using regular Software RAID, as it's more generally available.
  • With some fakeraid cards it's not possible to access the health status of your hard drives anymore (S.M.A.R.T.). Software RAID does not restrict you to do this.

Downsides too:

  • Dual boot with Windows will not be possible with software RAID with both OSs on the same array.
  • Accessing data from Windows or other OSs not possible. You'll simply need a Linux kernel to access your data.
  • maybe more, I can't think of more now
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