External SATA II Feasibility?

Posted on 2006-05-30
Medium Priority
Last Modified: 2010-04-03
I have a client that needs to backup a lot of data each evening.  We're using USB 2.0 to a large external hard drive.  It's working well enough except that they have so much to backup that it's not finishing before work the next day.

My question is:

Has anyone had any luck with a SATA 2 external hard drive?  I've seen a few controllers that have external SATA 2 ports.  I've seen a few SATA 1 external enclosures, but none that specify SATA 2.  What are the chances that a SATA 1 enclosure will work with a SATA 2 drive in it, and attached to an external SATA 2 port?

Also:  Can the drive be disconnected while the computer is functioning?  This may be the more important question.

If you have a suggested device or better solution, I'm all ears.

Thanks in advance,

Question by:tomgrazioli

Expert Comment

ID: 16790493
While the overall xfer speed for SATA 2 is faster than USB2, the real world xfer rate will be about the same.  The speeds given for each technology are maximum limits, not true transmission speeds.

Perhaps you can split the backup over different systems?  That would cut your time in half.

Expert Comment

ID: 16791554
Can you please explain this theory?  What you suggest would seem to indicate that even internal SATA drives would operate at the same speed as USB2 drives as the specification is the same, which is certainly false.

The drive can be disconnected, but should be done in the same manner as when disonnecting any other device, use the Safely Remove Hardware taskbar item to disable the drive before disconnecting so you won't lose any data.

Author Comment

ID: 16791978
I understand about "maximum tranfer rates".  If we accept the best case scenario as a benchmark, we'll have a basis for comparison.

USB 2.0 has a max throughput of 480 Mbps or about 60 Mb/second.  The max transfer rate of SATA 2 is 300 Mb/second.  Am I missing something about the true speed of SATA's?  Surely if they were not close to what they propose to be, it would be common knowledge and they wouldn't be flooding the market.

My thought is that an external SATA drive is no different than an internal drive.  It's just that the "ecable" extends out of the computer chassis and it uses a different power source.  

I know that removing an IDE drive while the computer is on can scramble a drive and lock up a computer.  I guess I'll have to experiment with a subordinate, external SATA drive.

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Expert Comment

ID: 16792248
First, be sure your SATA card is hot-plug, SATA II, and your HD is SATA II supports hot plug also. Get a card with an external SATA connector and ignore the cheap brackets.

If you get NCQ (Native Command Queuing), go for it - Is available from some providers and optimizes HD writes & reads (A bit like SCSI).

Go to drives properties using device manager. Search your external HD, properies, mark the HD as "Removable". Enable write cache on the unit (optimize for speed).

Before taking it out, be sure to "Disconnect" it like if it is a pendrive (with the green task bar icon). Sometimes you have to do it twice...

Good luck,

Expert Comment

ID: 16792377
I currently have a USB 2.0 HDD (LaCie by itself) and 4 Seagate SATA2 drives in RAID5.  I have used HDTach to benchmark the drives and have found that the SATA drives operate ABOVE 300MB/s (notice the capital B, SATA is rated at 300MB/s or 3Gb/s), while the USB drive runs around 30-40 MB/s (10x slower).  Now, I run faster than specs because of the RAID5 setup, but even that can't account for the order of magnitude increase in speed.  My RAID5 probably accounts for a maximum of twice the speed of a regular SATA drive by itself.
LVL 69

Accepted Solution

Callandor earned 375 total points
ID: 16793314

The speeds you are listing are interface speeds for maximum bursts, which only occur when the drive buffer is used.  After about a second, the buffer is emptied and the "sustained transfer rate" takes over, which maxes out around 60-80 megabytes/sec.  RAID exceeeds this because the total throughput of the array is measured, not a single drive, and a high quality RAID controller can reach 300MB/sec.  Note that even the ATA-100 and ATA-133 spec exceeds this, but USB 2.0 does not, with the overhead protocol taken into account, so you will likely benefit from using an SATA cable.  SATA is designed for hot-swap, so if you get a hot-swap caddy for the drive, you can make it removable.  Although SATA II has twice the interface speed of SATA I, it is only a burst speed and not a sustained transfer rate.  That said, SATA II does benefit from Native Command Queuing, which speeds up access in multitasking and multiuser environments.

SATA II drives tested: http://www.anandtech.com/storage/showdoc.aspx?i=2454
Previously asked question: http://www.experts-exchange.com/Storage/Q_21330145.html
LVL 30

Expert Comment

ID: 16800265
There are solutions,but they cost $$$.
What type of server?
Does it have a 64 bit 66 mhz slot?

The PCI buss maxes out @133mb /sec.
So looking at serial attached SCSI along with a fast system buss would be a start .
Otherwise I would look at a product like Live State Recovery from Symantec and have it do snapshot backups during the day,eliminating the need for a complete backup during the night.

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