HDD/raid question

[SilentDeath]

Everything seem better in dual.. dual cpu, dual vga etc... dual hdd?

Hdds have several platters so in therory two platters in one Hdd could be used independantly.
They would both spin together on the same spindle, as normal but there would need to be two seperate sets of actuator thingys to move the heads independantly.

This would mean you could have a RAID array that only takes the space of one drive and it could be compleatly internal to the drive and so not require two ports, acctually have some hope of using all the bandwidth of sata.


This must have been thought of before, so whats wrong with the idea?

[mike_w]

I think there might be a problem with repairs. If one half of the hard drive broke, it would be difficult to replace the broken half and rebuild the array. With normal RAID1, if one disk broke you can easily whack in another hard drive and rebuild it.

[SilentDeath]

I think there might be a problem with repairs. If one half of the hard drive broke, it would be difficult to replace the broken half and rebuild the array. With normal RAID1, if one disk broke you can easily whack in another hard drive and rebuild it.

Seems unlikely that one half would just break and leave the other perfectly intact.
One half would probably still work but would be very likely to fail once the other has, for the same reson.

I was thinking this would be a good idea for raid0. Having a raid1 mirror on the same spindle seems a bit pointless as both could easly die at the same time.
If you had 2x dual platter hdds you could do raid10 though.
Cant rememeber what the other modes do...

[Dougal]

Erm, most HDDs do have multiple platters

the 400GB Hitachi has 5 platters at 80GB each, the 500GB, 5 platters at 100GB each.

Thats how hard drives work.

[TooNice]

Indeed, but they are not read/written simultanously.

Personally, I think the problem would be reliability (or the cost it would take to make those drives at least as secure as current drives). Hard disks are highly mechanical, so adding such complexities could increase the risks of drive failures.

[SilentDeath]

Erm, most HDDs do have multiple platters

the 400GB Hitachi has 5 platters at 80GB each, the 500GB, 5 platters at 100GB each.

Thats how hard drives work.

All current HDDs afaik only have one voice actuator coil per drive, which means that each platter has to have it head in exactly the same place as all the others.

[Dougal]

The bottleneck is the drive controllers as well.

Unless they can get multiple streams through the cables at the same time its restricted. There is compression, which is where SATA 3GB/s is coming from

[SilentDeath]

Sata 3GB/s does not work by compression. They have doubled the frequency of the sata bus to give it the extra bandwidth.

Compared to the mechanical restirction, the controlers are nothing. They would need atleast an extra chip, if theres none available to do the task they could use FPGA's...

[badass]

Might seem silly but I thought that HDD's did write to all platters at once. Otherwise its a stupid waste of potential bandwidth.