[kwlug-disc] eSATA hot pluggable on Linux?

Khalid Baheyeldin kb at 2bits.com
Tue Jun 1 22:17:24 EDT 2010


On Tue, Jun 1, 2010 at 9:43 PM, unsolicited <unsolicited at swiz.ca> wrote:

> Khalid Baheyeldin wrote, On 06/01/2010 8:42 PM:
>
>  On Tue, Jun 1, 2010 at 8:07 PM, unsolicited <unsolicited at swiz.ca> wrote:
>>
>>  So why is it considered reasonable to have to shut down to change SCSI,
>>> or
>>> IDE, but not external SATA (which is actually exactly the same as
>>> internal
>>> SATA, with a bit more mechanical 'glue'.)
>>>
>>>
>> Because this is a hard disk dock that works with USB for removable disks,
>> and is supposed to work with SATA too.  It has the connector for SATA, and
>> provided a bracket and a cable as well.
>>
>> http://www.vantecusa.com/en/product/view_detail/295
>>
>> The reason I want SATA over USB is that the former is faster, and less CPU
>> intensive as well.
>>
>> The whole idea is to unmount a disk, power off the dock, and change the
>> disk. Works fine with USB, but not SATA (on my server).
>>
>
> Oh I get all this. Didn't you recently pick up on eSATA from me? (Some
> months ago.)


Don't recall that.

My first run in with eSATA was about 10 days ago when I bought that new
dock.
It came with a bracket that provides a port at the back of the server, and a
SATA cable inside the package.


>
>  The issue here is probably that the motherboard does not support the SATA
>> port multiplier feature
>> http://www.serialata.org/technology/port_multipliers.asp
>>
>
> Actually ... isn't it the motherboard's sata chipset that matters? -
> Everything else in Linux seems to depend upon chipset! (-:
>
> Which is to say ... would a cheap sata pci adapter, with an appropriate
> chipset, and port on bracket, rather than an entire new computer, be
> expeditious?
>
> I have several, from CanadaComputer, and been quite pleased. But not using
> under Linux at the moment.
>

Well, it is almost time for a new server, so been looking at a suitable
hardware for one, rather than get this one upgraded to a SATA that works.


> Also got an external enclosure. I think it took a whole 2 days before I
> separated the faceplate (guts) from the casing, and now just walk around
> with the bare drive and plug it in wherever I need it. (I think I actually
> accidentally bought a 2.5" enclosure, then discovered my drives were 3.5"
> and wouldn't fit. <sigh>) I haven't looked back, and never noticed the
> difference. It ain't pretty - but I don't care. Looks geeky, and that may be
> no bad thing.
>

The dock I got does both 2.5" and 3.5". I have to say the size/weight of the
2.5" vs. price/capacity is far better.


> Note - by extension - the drive doesn't have to be on your server. Given
> today's drive capacities, you can probably back up multiple computers to one
> drive. So set your scripts up, replicating to a drive off your desktop (at
> night), leave your server alone, and just deal with the desktop when and as
> you need to. [This is why I have gigabit throughout the house, and why those
> who say you don't need a gigabit gateway are wrong.]


Too much dependency on multiple machines being powered on. Failure if
something is not, ...etc..

Simpler is better: everything that matters is on the server, only it (and
the disk)
need to be powered up.


> By extension - a real 'bad' thing, bad filesystem driver, electrical spike,
> is less likely to take your backup out as a result of the same event. As you
> note on your web page - it doesn't matter if it takes 4 hours directly, or 8
> hours over your home network, when it's run overnight. And you'll be less
> distressed, perhaps not by much, at having to take your desktop down to
> detach your drive, than the server.
>

Well, there is the CPU spike too. I think it is USB that is the culprit, but
can also be wait for I/O somewhere (either dump itself, the disk, or USB).

Also, the first snapshot (from server's disk(s) to backup disk) better take
less time, since it means less locking time for locks on database files, and
whatnot. Better, not mandatory.

Data paranoia is not an affliction - it's a healthy lifestyle!
>
> They do, actually, thank you later!


Yes.

Many years ago, I had a break in and the computer was stolen, and the
tape drive was internal too!

Had I not had backups on tapes stored elsewhere in the house a full decade
of "stuff" would have been lost forever, irrecoverable.

I only lost one month's worth of data, which in the grand scheme of things
is far more tolerable than a decade's worth.

I bought another computer, another tape and was able to restore everything,
minus the one month.

Have been more data paranoid since ...
-- 
Khalid M. Baheyeldin
2bits.com, Inc.
http://2bits.com
Drupal optimization, development, customization and consulting.
Simplicity is prerequisite for reliability. --  Edsger W.Dijkstra
Simplicity is the ultimate sophistication. --   Leonardo da Vinci
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