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

[John Johnson]

I have no opinion or experience to share but thought that the following 
links might be helpful.

Ref: http://en.wikipedia.org/wiki/Chipset
Ref: http://en.wikipedia.org/wiki/Northbridge_%28computing%29
Ref: http://en.wikipedia.org/wiki/Southbridge_%28computing%29

Note: According to one of the above, IDE, SATA & USB are on the 
Southbridge chip.

JohnJ

On 2014-08-05 12:07, unsolicited wrote:
> 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?
>
>
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