[kwlug-disc] USB3 expectations?

unsolicited unsolicited at swiz.ca
Fri Jun 18 21:07:56 EDT 2010



Chris Irwin wrote, On 06/18/2010 4:40 PM:
> On Fri, Jun 18, 2010 at 14:31, unsolicited <unsolicited at swiz.ca>
> wrote:
>> So, now is there not only a USB3, there's a SATA3 (6Gbits/s,
>> 600MB/s effective)! And most drives can't keep up to SATA 1,
>> begging the question ...
> 
> As you had mentioned, SSDs are able to saturate SATA-II links
> already, so right there is a need (desire) for more speed.
> 
> Also note that since SATA-II you can have multiple physical devices
>  behind a single link (sadly not with all chipsets) whether it be a
>  simple port multiplier, or a virtual device backed by multiple 
> physical devices (Drobo, etc).

Interesting. Thanks, didn't know the multiple devices behind link bit.
Mind you, what else is a SATA card, that plugs into the PCI bus.

> I was just looking at a self-contained hardware RAID-5 enclosure.
> It works with SATA-II drives internally, but exposes itself as a
> single (large) SATA-III device. According to what I've been
> reading, using eSATA-III actually improve performance, as
> throughput of n-1 disks is more than SATA-II can handle (and also
> apparently more than PCI-E 1x can too). This is with plain-old 7200
> RPM rotational drives. So there is definitely existing capability
> for exceeding SATA-II throughput.

Interesting. But then, this is largely no different than SCSI - for
RAID 5, let alone external, you're looking at a SCSI host adapter,
also interfacing with the motherboard. i.e. Any RAID or external
controller is going to be able to saturate whatever link is used, be
it SCSI or SATA. Evidently, perhaps no longer true with SATA III.

>> So what does it all mean to you and I, the home consumer, or to
>> business?
>> 
>> - SCSI will become even less popular, given the higher cost than
>> SATA, as SATA performance improves, in (large?) RAID arrays /
>> shelves?
> 
> SAS still has benefits for some use cases. Price is not one of
> those use cases, though :)

Right, redundancy, etc., etc., but my point was that with SATA getting 
faster and faster, it must be getting harder and harder to justify the 
price difference of SCSI against the performance differential.

> Lenovo (and some other manufacturers, apparently) are starting to
> use eSATA/USB2.0 hybrid ports. It doesn't take any more room, and
> laptops have SATA for the internal hard disk already anyway. I'm
> not sure if there are any differences in USB3.0's port design that
> would cause problems. I can also see this as a market/price
> differentiation feature ("consumers don't need eSATA")

Well the ()'s a crock. (-:

> http://gallery.techarena.in/data/513/367.jpg

Now THAT's interesting. Powered eSata. I suppose this is what makes 
docks viable.

>> - OpenWRT devices won't get eSata (typically?) or USB3, the
>> processors not (typically?) being able to keep up to the drive?
>> Vis a vis NAS?
> 
> Your NAS will throttle on gigabit ethernet before SATA-II.
> 
> What do you need that sort of disk throughput on your openWRT
> device for (not criticising, just curious)?

Well, one promise of such devices is the USB, and so you expect to 
hang a TB or 2 off of it as a NAS / backup repository for the network. 
Let alone a multi-drive external unit. But, I understand wailing away 
on it will largely bring the device to its knees. Sorry, I don't 
understand that, I saw references to it. I have no actual knowledge of 
that one way or the other.

>> - the benefits of USB3 or SATA3 will largely only be felt by
>> multiple drives feeding multiple servers that feed multiple
>> clients (e.g. SQL). Even if the clients are all connected
>> Gigabit, the net will still be the limiting factor?
> 
> I think USB3 will be felt by regular consumers. Flash drives are
> slow, usb3-attached SSDs would be awesome.


>But not at current SSD
> prices...

Agreed.

But, vis a vis eSata, why go down the USB road? OK, I know, no eSata 
port. But also, likely, no USB3 port.

Internally, be it internal flash drive or bay, you know it's going to 
be SATA based, not USB based.

> SATA-III will also benefit "Small" virtualization users with
> on-host storage. "Big" virt users will have centralized network
> storage (and thus still benefit according to your rule above), but
> us smaller guys running multiple VMs locally will potentially see a
> benefit.

Right, I get the whole SATA III thing, if drives are a bottleneck, 
it's the USB3 thing that nobody's said 'Why?' over eSata, yet.

>> - even on a home connected web server, the limitation will be ISP
>> speed, not disk speed? IIRC, typically systems are disk bound,
>> but there's a whole lot of 'stuff' between the CPU and disk,
>> preventing an increase in disk speed from providing an equivalent
>> increase in system speed? (And this is even presuming sufficient
>> requests are coming in sufficiently often to "make 'it'
>> worthwhile"?
> 
> I use unison to sync $HOME between my laptop and server. It runs on
>  both local and remote hosts, examines my data on each, then
> presents a merge-list (which it executes using an rsync-like
> method). The part where my two $HOME directories are being examined
> takes more time (by far) than the actual data sync over the network
> (even using wifi). Faster disks on my server, even given the 'slow'
> network link, would still be a benefit.

Hold on, is the issue there disk speed, or CPU speed calculating the 
deltas?

>> - if drives are SATA, and the bus is USB3, why USB3 instead of
>> just staying with (e)SATA?
> 
> Getting a USB3 enclosure for your drive would allow backwards 
> compatibility with USB2 hosts -- granted, most eSATA enclosures
> also have USB2.0 ports anyway. Some SATA chipsets don't like hot 
> unplugging.
> 
> eSATA drives need a separate source for power, versus one
> power+data cord for USB.

Right, but your .jpg above shows that ain't necessarily so.

And I'll bet they become rather popular, rather quickly, for just that 
reason.

So, the USB / firewire 'next level' race is back on, but joined by 
eSata now.

Dunno, but 640k oughta be enough for anybody sounds not unreasonable, 
some days.



More information about the kwlug-disc_kwlug.org mailing list