[OT] Connecting two hard drives on same IDE cable

[Mikkel L. Ellertson]

Dotan Cohen wrote:
> On 29/08/2007, Mikkel L. Ellertson <mikkel at infinity-ltd.com> wrote:
>> One other thing to think about - if you do not have optical drives,
>> or if you have fast access optical drives, it can be beneficial to
>> have each hard drive on its own controller. Unless you are stuck
>> with one of the controller that does not allow access to both IDE
>> interfaces at the same time, or does not support fast access on both
>> interfaces, it can speed up overall disk access. This is especially
>> true when copying or moving data between drives.
>>
>> Mikkel
> 
> Are you suggesting that for a situation with 2 IDE interfaces on the
> motherboard, two optical drives and two hard drives that each IDE
> interface have one each hard drive and optical drive? That seems to me
> would slow down the optical drives, which are faster than the hard
> drives, as the IDE interface would run at the speed of the slowest
> device on the interface.
> 
> Dotan Cohen
> 
In my experience, optical drives tend to be slower then hard drives,
not faster. But the important part are the data transfer rate, the
IDE chipset, and what you are accessing. If the hard drive and
optical drive both have the same max transfer speed, or the
interface can use different rates for each device, then it can be an
advantage because most system do more hard drive access then optical
drive access. (Take a look at the DMA modes supported by the better
double layer DVD drives...) As long as the optical drives do not
force a slower transfer rate for both devices on the cable, and you
do not do a lot of reading/writing to/from the optical drive, it can
speed up hard drive access. (Not the timing reported by hdparm, but
real world access when accessing both drives at once.)

There are a few things to watch out for:
 Writing data to an optical drive on the same interface as the drive
the data is coming from may be a problem, especially if the optical
drive has a small buffer.
 Connecting a slower transfer speed optical drive with a fast hard
drive when the interface does not support different speeds for
different devices.
 Cases where you have heavy optical drive access.
 Broken IDE chipsets that do not support data transfer on both IDE
interfaces at the same time.

You have to know your hardware, and your usage, to know if this
configuration will be helpful to you. Even when you only have 2 hard
drives, and no optical drives, it will not help if you have to
serialize command to the IDE interface, or if the second interface
does not support the faster transfer rates that the drives do. Then
again, if you are using SATA drives, none of this applies anyway.

Mikkel
-- 

  Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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