Asus P5B-E does not detect external eSATA disk enclosure or its disks

Protip: Connect the internal JMB363 SATA connector towards the rear of the motherboard to an eSATA port bracket and ignore the integrated eSATA port to avoid both of the following problems.

I plugged in an eSATA disk enclosure to a Asus P5B-E LGA775 motherboard and it’s ignored!

This one’s easy.  Since the integrated (I/O shield) eSATA port is connected to the auxiliary JMicron JMB363 SATA RAID controller:

  1. Set “JMicron SATA Controller Mode” to AHCI in the BIOS.
  2. Unplug anything you have connected to the PATA (80-pin rectangular) connector.  If anything is plugged into this connector, the eSATA port will be disabled.

Sure would have been nice if the manual had mentioned that second detail, eh?

I plugged in an eSATA disk enclosure to a Asus P5B-E LGA775 motherboard and all of its disks except one are ignored!

Serial ATA has a PMP (Port MultiPlier) mode which allows the signals for multiple physical SATA ports to be multiplexed over a single physical SATA link.  The tradeoffs are:

  • The operating system SATA driver must support SATA PMP mode
  • Both the SATA controller and the disk enclosure must support SATA PMP mode.

In this case, the OS (Linux), the controller (JMicron JMB363) and the disk enclosure (Sans Digital TR5UT with JMicron JMB393) all support SATA PMP mode.  But only the first disk in the enclosure is available to the Linux kernel.

So what’s the problem on the P5B-E?  Simple: the integrated JMB363 eSATA port does not support PMP mode and will only communicate with the first disk in an external enclosure (or a single logical device, in the case of an enclosure with an integral RAID controller like the Sans Digital TR5UT.

The solution: connect an eSATA port bracket to the JMB363’s internal SATA connector, which does support PMP mode.  Then all of the disks in the enclosure will be available.

Sure would have been nice if the manual had mentioned that, eh?

Using multiple independent disks in a external enclosure on the Asus P5B-E is so slow!  Who took the ‘express’ out of PCI Express?

JMicron did, unfortunately …  The JMB363 was designed with SATA port multiplier (PMP) functionality, but for some reason, the design only included a single lane PCIe 1.x link to the host.  It takes only two SATA HDD devices (100-150MB/s sequential read/write capacity) to saturate the JMB363’s 1x PCIe link, which has a theoretical maximum capacity of 250MB/s.  More than two HDD devices only gets worse (and we won’t even talk about SATA SSDs …)

Unfortunately, there’s no good news for the P5B-E; the Intel ICH8R southbridge does not have PMP functionality; it was introduced in ICH9R.  If you need to connect more than 8 HDDs without everything grinding to a halt (for example, during an array conversion), you’ll have to look for another solution.  (I chose to send the array data over the network and write to the disks while attached to another machine without these limitations.)


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