HDD Speeds (ATA UDMA etc.)

[q2418130103p]

Could someone explain to me what the differnences in speeds for all these hdd's are. What is currently the fastest. I hear that with UDMA there is a lot less cpu usuage.

I'm just alittle confused. I'm seeing ATA100 drives selling for less then DMA66 drives. So I'm guesing there is a lot of goodness with DMA.

Any light on the subject would be great.

Thanx,
Jay

[bailey]

ultra dma is the burst transfer rate for a drive, not its speed.

for better drive activity you will want the fastest rpm

a 7200rpm drive would perform faster than a 5400rpm drive.

and yes the ata rateing does make some differance too, but the rpm would be more noticeable.

I am sure there are otheres here that can explain it to you in better terms, but basicly that is what it amounts to

[q2418130103p]

Can a drive be ata and dma at the same time? What's the differnence, and why do you never find them both in the same drive.

And also, whats with Ultra ATA and Ultra DMA?

[Blakhart]

In short, I view ataxxx as the theoretical data burst speed of the drive when first acquiring data. DMA is just that: Direct Memory Access. The drive doesn't have to bother the cpu to send or receive data from the mem. As a bit of trivia, I had a ata100 drive that would peak at 160 mbs for a few ms when first accessing.
That was on a AMD751 chipset. The AMD751 is a ata66 board. Them was the days.
A drive can be ataxxx and dma at the same time but it depends on the drive, the mobo and the os. The mobo will determine the ata speed as the speed is hard set in the chipset. If a drive is running less than the mobo's ata, the mobo will lower its expectations accordingly. Read up on the various levels of dma.
Just some thoughts

[theENiGMA]

ATA and UDMA are used interchangeably. THey are drfferent things, but, if a drive says it is ATA66 or UDMA66, that means it can transfer data at 66mb/s. Same with 100 or 133. THe fastest sdrives out right now are ATA (or UDMA) 133. In order to use it to it's full potential, your motherboard must support ATA133. If it doesn't, the drive will still work, but only at whatever speed your motherboard is rated at. It's all fully backward compatible.
-KEiTH

[q2418130103p]

ic. That clears up a few thing.

So what would you guys suggest for running two 40's on raid (I mean speed and data tranfer rate)?

[glc]

The actual speed and access time of a drive has more effect on transfer rate than the UDMA or ATA xx rating. I would say that ATA-100 is plenty, but make sure the drive is 7200 rpm and has an access time of less than 10ms.

As an aside, I'm not a big fan of IDE RAID - the increased potential for data *loss* outweighs any speed increase in my mind.

[q2418130103p]

Yikes! data loss? Literally?

[glc]

It all depends how you set the raid up - if you have mirrored drives you have redundancy but no speed increase, and half the capacity. If you stripe the drives you get a speed increase but if ONE drive craps out you lose EVERYTHING. You need 4 drives to do a mirror AND stripe to get redundancy and speed increases.

[q2418130103p]

So its really just not worth it eh?