I had two queries with regard to PATA drives and experiecnes. I seem to be going around in circles so any help would be greatly appreciated.

 

The first is whether from everyones experience a PATA drive is suitable to act as the cache drive? This would be, I presume, in comparison to using a SATA equivalent.

 

The second is whether it is possible to place two PATA drives (not cache in this example) onto the same channel/cable and whether the array itself or performance takes a dramatic hit.

 

Any experiences would be fantastic and much appreciated.

 

-Alex

I had two queries with regard to PATA drives and experiecnes. I seem to be going around in circles so any help would be greatly appreciated.

 

The first is whether from everyones experience a PATA drive is suitable to act as the cache drive? This would be, I presume, in comparison to using a SATA equivalent.

 

The second is whether it is possible to place two PATA drives (not cache in this example) onto the same channel/cable and whether the array itself or performance takes a dramatic hit.

 

Any experiences would be fantastic and much appreciated.

 

-Alex

You will be fine with a PATA as a cache drive.  Regardless of the drive used, your network will probably be the bottleneck for write speed.

 

Same with more than one PATA drive on a channel.  If possible, if using a PATA parity drive, put it on its own cable/channel.  You are limited by rotational speed of the disks FAR more than multiple requests on the same cable.  In the same way, you are limited by the PCI bus limit of 133MB/s when performing a parity check/initial calculation on a large number of drives than the number of disks on a specific cable. 

 

If you have the luxury of a lot of PATA ports, then spread the load of the disks... it will probably make a small difference.

Cache on P-ATA should not be a problem.

Parity on P-ATA should not be a problem (but it's not recommended to share this cable with other data drives).

 

Multiple drives on one P-ATA will eventually lead to a problem.

 

1. Performance. The CPU can only talk to one drive at a time on a P-ATA cable.

    So while a request is made to the master, a request cannot be handled or sent to the Secondary.(and vica versa)

    It's not like SCSI, where the CPU could disconnect from the request and get an interrupt when the request was ready.

 

2. If one of the two drives on a P-ATA fails, it can take the the whole bus down. This will lead to multiple drive failures.

    I've had it happen on a RAID5 array. It will happen sooner or later with P-ATA.

    What I've done on the past was use multiple promise P-ATA controllers and only put one drive on a cable OR...

    I would do RAID1, but insure that it's sibling was on a different controller or cable.

 

3. If you choose to use P-ATA drives and multiple drives per cable.

    Try to stagger how they are used on a cable. so that each consecutive read goes to another cable or controller before the second drive on the cable is accessed. This will not prevent a multiple drive failure (Which by the way WILL HAPPEN and it's ONLY A MATTER OF TIME).

it will allow faster access to the drives as a controller can be accessed in parallel (where multiple drives on one P-ATA cable cannot).