Kevin Keane wrote:
>> -----Original Message-----
>> From: John Drescher [mailto:drescherjm AT gmail DOT com]
>> Sent: Friday, November 13, 2009 5:06 AM
>> To: Bruno Friedmann; bacula-users
>> Subject: Re: [Bacula-users] eSATA / USB disks as media for Bacula
>>
>>     
>>> Just an add to the previous great comments.
>>>
>>> If you envisage to use e-sata, check that your chipset/bios support
>>>       
>> hot-replace/add.
>>     
>>> It's working nicely with laptop, but not always for a vaste majority
>>>       
>> of "cheap" motherboard.
>>     
>>> Mine a Asus M2N-Pro support e-sata : but only on cold restart
>>>       
>> (jmicron and 2.6.27 kernel)
>>     
>>> Sadly I've to use the usb-2 ...
>>>       
>> I am pretty sure the regular SATA ports on this board (nvidia chipset
>> ones) support hot swap. I say that because I have 3 or 4 of my linux
>> raid servers at work using M2Ns and I have definitely hot swapped
>> drives on them.
>>     
>
> I am by no means an eSATA expert, but my understanding is that the real issue 
> is IDE emulation and (Windows) driver support.
>
> Based on that understanding - which could be wrong:
>
> IDE mode = no hot swapping
> AHCI mode = hot swapping
>
> At least assuming that AHCI is implemented according to proper specs - which 
> may or may not be true for cheap motherboards.
>
> AHCI needs to be enabled in the BIOS, and ALSO needs to be supported by the 
> hard disk driver in your operating system. Windows 7 and I believe also Vista 
> have AHCI-capable drivers, but Windows XP doesn't out of the box.
>
> In the Linux world, I really don't know - I believe that it would be slightly 
> ahead of the curve and probably have a bit better AHCI support.
>
> Unfortunately "I have hot-swapped drives" is not a reliable measure. It is 
> entirely possible that hotswapping worked purely by chance but would break 
> the next time you try it.
>
>
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>   
It's been a while since I read up on the difference between eSATA and 
SATA, so take this with a grain of salt.  That said - big point I 
remember taking away from that effort was that eSATA HDDs provide an 
extra bit flag that informs the OS, drivers, firmware, etc. that info 
sent to that device should not be cached - it should be synced to the 
device immediately.  There are other points like length of cable and EMI 
shielding, but the "always commit my data" flag was the big one I found 
most important - especially for hot swapping

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