[kwlug-disc] Multi-bay docks ... 1 at a time??? [Was: Re: Linux-compatible eSATA expansion cards]

[unsolicited]

On 14-06-30 09:53 PM, Khalid Baheyeldin wrote:
> On Mon, Jun 30, 2014 at 8:09 PM, Paul Nijjar <paul_nijjar at yahoo.ca> wrote:
>
>> In an ordinary situation, maybe. However, in this computer I am
>> planning to use all the internal SATA connections for other drives.
>>
>> Honestly the differences between eSATA and SATA still confuse me, even
>> after reading the Wikipedia article. Is it true that not all SATA
>> ports on a motherboard can be converted to eSATA with these
>> connectors?
>
> One important difference is hotpluggability.
> This depends on your chipset. There is a table here listing the supported
> chipsets.
>
> https://ata.wiki.kernel.org/index.php/SATA_hardware_features
>
> That page also lists PMP, if you want to attach more than one device to the
> same eSATA cable. Although, when I tried it with a dock that has 2 drives,
> one drive would have normal speed and the other would be really slow.  ...

Summary: Am I understanding the availability of possible solutions to 
moving vms between computers (especially future laptops - single esata 
port / USB 3 availability / no PMP controller) correctly?


Happened to poke and google around the web on this over the weekend. 
Playing with vbox and wanting to move vms around my internal net - 
leading to the need for GBs of extra space on both source and 
destination. Over my net, ~35GB vm takes just over an hour to copy, slow 
machines. Fast machine on one end about 1/2 hr. Same for machine to 
external drive on USB 2 (to and from -> 1 hour). So happened to poke 
about docks / what they and storage might cost. Idea of USB 3 / SSD is 
attractive, but seems cost prohibitive. Also leads to the idea of 
running the vm off external device, and schlepping to different 
computers as needed. e.g. Hardware failure. Even if I don't have USB 3 & 
eSata on every machine today, presumably each new machine will at least 
have USB 3.

Given Khalid's note above that points out that dual-bay docks are 
essentially pointless (more than 1 drive, slow on other drives), I 
wondered why / what's up. Seems like whatever (multi-bay) such is 
plugged in to must be -TO- a port multiplying sata controller or this 
slow drive problem is run in to. Since PMP isn't required for a sata 
controller, most everyone will be out of luck unless they know to 
specifically search for such capability beforehand. (Making it seem like 
multi-bay docks are are marketing ploy - most things you might connect 
to can never take advantage of it?)

Seems that only 1 drive can be talked to at a time (Command Queuing?) / 
something PMP must be in the sequence to do the 'multiplexing'(since any 
one drive can't saturate a SATA link unless it's an SSD) to try to keep 
the link to the computer going full bore.

Yet it does not seem that PMP is available at the device 
(dock/adapter/drive) end - it has to be in the controller, and I expect 
its unlikely for laptops to have them. Does this not:

- render multi-bay docks pointless (unless a 'duplicator' or RAID)?

- make simple adapters attractive e.g. 
http://www.canadacomputers.com/product_info.php?cPath=95_96&item_id=35385P 
more sensible - except still have problem of providing power to drive if 
large capacity / 7200 RPM? (Let alone, not normally stocked?)

- if eSata, 
http://www.amazon.ca/eSATA-External-Bridge-Adapter-Converter/dp/B00DHCC7NQ/ref=sr_1_2 
or 
http://www.amazon.ca/Anker%C2%AE-Uspeed-Converter-Adapter-External/dp/B006J2L0ZM/ 
?

- render eSata useless vis a vis USB 3. i.e. New laptops will not likely 
have multiple eSata ports - if any at all, but will likely have multiple 
USB 3 ports (yet USB can do the multiplexing itself so no need for PMP?)

- make NAS / RAID-JBOD units make more sense as it will be managing the 
(single) link to computer flow? Yet the point of adapters/docks is quick 
disk flipping about, rather than digging into a (NAS) enclosure!

- unless a laptop, live with digging into the case when moving drives 
around. Back to advantage of cages, e.g. 
http://www.icydock.com/goods.php?id=175

So, it seems a single bay dock is the only thing that makes any sense, 
and if multiple drives are needed, purchase multiple single bay docks.

Yet I see 3TB limitations on drive sizes for such, and 6TB drives are 
now here, with 8TB drives soon to come. I do see that 
http://www.canadacomputers.com/product_info.php?cPath=14_679&item_id=047936 
notes 'Up to 6.0 TB*', but it is not clear that that does not mean MAX. 
3TB PER BAY!

I'm guessing this has more to do with the USB chipset in use only able 
to understand MBR drives, not GPT.

Seems like a net. NAS makes more and more sense, but schlepping GB of 
images over the 2Gbps network vs local 6GBps sata III seems 
counter-intuitive.

Am I understanding the availability of possible solutions to moving vms 
between computers (especially future laptops - single esata port / USB 3 
availability / no PMP controller) correctly?