Change from Onboard SATA to PCI-E SATA can keep array valid ?

Ronan C

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20 minutes ago, Ronan C said:

i want to move from my 6 sata ports of my XEON motherboard to this new PCI-E controller, how this can be done

Very easily done.  UnRAID tracks disks by serial number not by controller connection or SATA port.  You should keep any SSDs attached to motherboard SATA ports for TRIM support unless your PCIe controller supports this; most do not.  Unless your new PCIe controller does something to mess with the disk serial number reporting (some RAID cards can do this) you should not have any issues.


When I bought a PCIe controller, I just removed HDD SATA cables from the motherboard ports and plugged a forward breakout cable from the the PCIe controller into the SATA ports on the HDDs.  The array configuration did not skip a beat.


If you have dual parity, there may be some other considerations (I am not an expert on this) but with single parity it is very straightforward to just move the connections.

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On 12/7/2022 at 2:21 PM, Ronan C said:

Its a very cheap controller,

Yes, it is cheap and your performance will be very poor with multiple hard drives attached. 

  • One PCIe 3.0 lane split among however many drives are attached
  • 1 GB/s bandwidth (PCIe 3.0 x1) total in the best case
  • Figure a 20% loss due to system overhead leaving you with 800 MB/s actual available bandwidth.
  • If you have even 8 drives attached to that controller that is 800/8 = 100 MB/s per drive. 
  • Most modern HDDs are capable of ~200 MB/s

When you are doing a parity check, disk rebuild, etc. all drives will be active simultaneously and if you have 8 drives attached to that controller, you will be getting a max of 100 MB/s on each.  If you have more drives, then even less.  16 HDDs attached would give you a maximum of 50 MB/s


My last parity check completed at an average of 159 MB/s and it started at close to 200 MB/s.


As mentioned by others, port multipliers (JMB575 chip on that card) are not recommended for use with unRAID and that card has four of them.

Edited by Hoopster
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1 hour ago, Ronan C said:

I totally forgot to check about PCI-E version

PCIe version 3.0 is fine.  In have a PCIe SATA controller that is only PCIe version 2.0, so half the bandwidth of 3.0.  However, that is more than enough for the 8 drives I can attach to the card because it is an x8 card which leaves me with 400 MB/s for each drive.  It would not be great for SSDs but only attach HDDs to the controller.


In your case, if you really want to attach 16 drives, you need to be looking for at least a PCIe 3.0 card that is x4 or greater.  PCIe 3.0 x4 would give you 4 GB/s (figure 3.2 GB/s after overhead) which is 200 MB/s for each of 16 hard drives.


See the forum discussion linked above by @ChatNoir for recommended controllers.

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