Comparing SCSI and ATA drives
Dorian Cougias
11.06.2003
Rating: -4.00- (out of 5)
There's
pretty much no difference in interfaces or bandwidth between any of the
SCSI or ATA scenarios as both use DMA to transfer data to and from the
CPU. Serial ATA is reaching the speeds of Ultra SCSI, and every format
except the older parallel ATA are hot pluggable, with both serial ATA
and SCSI supporting both internal and external formats.
ATA and SCSI supporting both internal and external formats.
| Parallel ATA | USB | FireWire 800IEEE 1394 | Serial ATA | SCSI |
| Connectivity Market |
Internal storage |
External storage |
External storage |
Internal and External storage |
Internal and External storage |
| Cost comparison |
Base |
> Parallel |
> Parallel |
= Parallel |
> Parallel |
| Speed |
100 |
60 |
100 |
150 |
160 |
| Bootable (Win) |
Yes |
No |
No |
Yes |
Yes |
| Bootable (OS X) |
Yes |
Yes |
Yes |
Yes |
Yes |
| Hot Pluggable |
No |
Yes |
Yes |
Yes |
Yes |
| Cable Lgth (m) |
.45 |
6 (per link) |
4.5 (per link) |
1 |
12 |
SCSI and ATA comparisons
There is a significant difference in price and warranty between the two
though. Let's look at the differences between an ATA and SCSI drive
from the same manufacturer -- Maxtor.
There is a significant difference in price and warranty between the two
though. Let's look at the differences between an ATA and SCSI drive
from the same manufacturer -- Maxtor.
| Type | Capacity | Speed | Price | SMART | Warranty |
| DiamondMax ATA |
80.0 GB |
133 MBs |
88.24 |
Yes |
1 year |
| Atlas 10K III SCSI |
73.4 GB |
160 MBs |
279.77 |
Yes |
5 years |
Individual drive comparison
Funny enough, the capacity is slightly smaller on the SCSI drive than
the ATA drives (which is due to formatting differences between the
two). The ATA drive is slightly slower than the SCSI drive. If the
differences were only these two items, I'd say it was a wash. But, the
real differences come in with the price and the warranty.
Any sane network administrator is going to have at least 1 spare
drive for every 10 drives in use so that when one breaks, the spare can
be grabbed from the shelf and immediately put into use while the
original is being shipped back under warranty.
To even things out between the warranty differences of one and five
years, we'll say that the administrator will have to replace each of
the ATA drives 1.5 times over the five year period.
| Type | Originals | Spares | Replacements | Cost |
| SCSI |
10 drives |
1 spare |
0 |
$3,077.47 |
| ATA |
10 drives |
1 spare |
15 |
$2,294.24 |
Price differentials
Even with the drive replacements, the costs of the ATA drive format are
still less over a five-year period than the cost of the SCSI drives.
And that's just for single-drive implementations. What about mirrored
drives or RAID arrays? If we extend the argument above, this time
adding the additional drives for mirroring or RAID 5, plus the hot
spare for the RAID 5 system, we can still see that the ATA arrays are
going to be less expensive (even allowing for failure) over the long
run.
| Type | Originals | Hot Spare | Add'l Spares | Replacements | Cost |
| Mirrored SCSI |
2 drives |
-- |
-- |
-- |
$559.54 |
| Mirrored ATA |
2 drives |
-- |
-- |
3 |
$441.20 |
| RAID 5 SCSI |
5 drives |
1 |
-- |
-- |
$1,678.62 |
| RAID 5 ATA |
5 drives |
1 |
-- |
9 |
$1,411.84 |
RAID price differentials
So what's the real difference? You'll be replacing more drives more
often. Which means that you'll want to know a lot more than you know
now about SMART reporting (our next article) and drive management
strategies.
|
Technical Update 
