Newsgroup: it.comp.hardware.storage
Titolo: SATA controller hot swap?

I was trying to set up a network storage box and I have a question about 
what SATA controller I might need.
I'm looking at an Asus P5RD1-V motherboard and it has 4 onboard SATA 
channels.  I want to hot-swap the drives though, and cannot find anything in 
the documentation that says whether I can do that or not.
I have hot swap bays for the drives, but is that all I need?  Is whether or 
not you can hot swap a drive dependent on the physical connections (which I 
have covered) or is it a feature that the controller must support?
My confusion comes in because the SATA spec says that SATA is 
hot-swappable... so shouldn't every controller follow the spec and be able 
to have drives swapped?
Of course, this comes down to a money issue.  I have a motherboard with SATA 
onboard, but do I really need to buy a $300 card on top of that to hot-swap?
--
Shawn Wilson

 onboard, but do I really need to buy a $300 card on top of that to hot-swap?
Nope. 

 Yes, and that's why Asus doesnt say anything about it, it comes with SATA.
So would it be 'safe' to buy any SATA controller and expect it to work?
The thing that gets me is simply that when I look for say 4 port cards, I 
find a no-name card for $22, a HighPoint card for $88, and a Promise card 
for $209 that don't mention hot-swap.  Then I find a $288 Adaptec and a $300 
3ware that specifically mentions hot-swap.  That suggests to me that there 
is something 'special' about those controllers.  Now, maybe that's just the 
lemming 'get what you pay for' in me, but what drives a card from $22 to 
$300?
Besides what company one might like better or expect better support from, 
why is there such a huge price difference if they all do the same thing? 
(and by the same thing I mean having 4 ports, raid 0/1/0+1, and presumably 
hot-swap)
When I look at RAM I can buy Kingston valueram for $100 or Crucial for $150 
(hypathetically) and know that if the cas timings are the same I'm simply 
paying for quality and potential longevity.  That price difference makes 
sense.  The price difference on SATA controllers does not, at least not to 
me.
Lastly, most of the 8 port cards are 64bit cards.  I only have 32bit PCI 
available.  Someone said they'll still work... is that true?
--
Shawn Wilson 

 available.  Someone said they'll still work... is that true?
    Call the manufacturers and ask them.  Better yet, email them.
    At least with email, you'll have a trail, and they'll know it.
*TimDaniels*


It is like asking, is SCSI hot-swappable?
Yes and no. Depends on particular implementation.
And on the meaning of "hot-swappable".
Provide more details for more accurate answer.

 available.  Someone said they'll still work... is that true?
You said your motherboard supports SATA, so why do you need a card at all ? 

 Its part of the SATA standard, so you always can.
Nonsense. SCSI is hotswap too but not all SCSI support it.
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 so shouldn't every controller follow the spec and be able to have drives swapped?
Since it doesn't have latches that activate and prevent you from physically swapping
the drive that probably just means that there is a mechanism in place that the driver
can pickup on and notify the OS and applications that a drive was disconnected
(or re-connected).
Whether drive swap is actually working depends on whether the card's driver 
dynamically reports a swap and how the applications and OS react on that.
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Yes, if the PCI slots are not keyed for 5V.

 Nonsense. SCSI is hotswap too but not all SCSI support it.
Thanks for that completely superfluous proof that you cant
even manage a viable troll, or anything else at all, either.
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I am actually dealing with 2 machines, one with 4 SATA ports onboard (Asus 
motherboard - and Asus confirmed that theirs are hot-swapable) and one 
without SATA onboard because I need 8 ports in that one.  I didn't elaborate 
that before because I didn't feel it was needed information.  The card would 
be for the machine without on-board SATA.
--
Shawn Wilson 


'if the PCI slots are not keyed for 5V' it will work?  Meaning that my slots 
must be 3.3V(guessing from memory) for 64bit cards to work in a 32bit slot?
--
Shawn Wilson 

 And on the meaning of "hot-swappable".
Hot-swap means ability to replace a failed component with a good device in a
fault tolerant system, without causing disruption to an operating computer.
If you want to hot-swap a hard drive, then you need to have a RAID system.
It is up to your RAID implementation to manage a rebuild process.
Physical removal and addition of powered on HD, requires a special
electrical (and mechanical) conditions to be done safely. Normally power and
signalling connectors are combined, with a special care given to contacts
length and positions. It is done to ensure a proper sequence of establishing
contacts (ground, power, data) during plug and unplug operations.
Mechanically, connector(s) are placed on a backplane and special guide rails
and latches are designed to facilitate a smooth and reliable disk
attachments and detachments.
So, you need a RAID compliant controller or Operating System for software
RAID - to perform rebuild; and a hard disk enclosure (backplane and disk
trays) which support hot-swapping. SATA drives and SATA controller are not
enough.

 wrote
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Sometimes I just assume that others will assume and I guess that's far too 
many assumptions.
I'm well aware of the need for RAID and the proper hardware to accomplish a 
hot-swap.  Those things have explicit documentation and guidelines readily 
available.  What isn't well documented or known is whether all SATA 
controllers are by nature able to be used in a hot-swap situation assuming 
all else is capable (the drive, physical bay, os, etc...)  I'm trying to 
decide on a controller and cannot as of yet come to a conclusive choice.
My setup includes a server rack-mount case with 8 front 5 1/4 bays filled 
with drive swap trays.  The setup will include 6 drives for now, 2 being 
part of one set and 4 being part of another set.  The set of 2 will be a 
RAID 1 mirror set, and the set of 4 will be a 0+1 striped set of 2 mirrored 
to the other 2.  The idea is for the mirror drives to be swaped on a 
schedule to have an off-site duplicate of our data.  The 2 drive set would 
be swapped every day and take place of 8 of our current tape drive based 
daily backups.  The 4 drive set would be a place to store whole machine 
images, and an archive history of files so we could recover last week's 
version of your documents.  This is intended to be a NAS device that will 
replace all of our tape backups and expand our backup/restore capabilities.
I'll be using SATA 150 drives at 400G each for now giving us a daily 400G 
store and a long term 800G store.  All in all I'll have 2.4 TB online with 
1.2 TB effective (since it's all mirrored).  And of course with the room to 
add two more drives to the long term storage to bring that up to 1.6 
effective.  Did I mention that the price tag is currently under $3,000.  The 
same setup from Dell is around $12,000.  Granted, they use SCSI 320 drives 
at over $1,000 each - but my concern is total space, not per second speed. 
Backups have 8 hours at night to run over a dedicated Gigabit ethernet 
subnet, I wouldn't care if it took only 1 of those hours instead of 3. 
That's not worth $9,000 to me.
Basically, the bottom line is that unless I can confirm from the 
manufacturers mouth that their card is capable, I'm on my own crossing my 
fingers, although chances are good that most anything I get will work.  I 
would have thought that it would be more concrete than that, but in reality 
it doesn't seem to be.
Case in point:  In my personal computer I'm running an nForce2 board with 2 
on-board SATA ports.  The online manual, the website, nor the reseller had 
any note of it being RAID capable.  I found a user online with the same 
board who said it was.  I took a chance, and when it arrived the box nor the 
manual made any mention of RAID, however upon boot, there it was.  The RAID 
controller clearly announced itself and I'm running a nice and fast striped 
set for my system and game partitions.
SATA RAID and hot-swap capabilities (as far as controllers are concerned) 
are just as inconsistent as USB used to be with their 'high speed' vs. real 
'USB 2.0' support.  I remember reading that there was no official rule 
stating how to label 2.0 vs. 1.1 for a time and some hardware makers would 
label products 'high speed' that were not truly USB 2.0.
It should be required on all SATA controllers to not just omit things like 
hot-swap or RAID, but to expressly note when either is not applicable.  Not 
showing RAID or hot-swap in the description is not as intuitive as saying 
RAID: NO / Hot-Swap: NO.  That responsibility probably lies with the 
hardware reseller and I've not found one yet that does it that way.
In the end, I think I've gotten the help I need from the community and I 
thank you all.  I have to rely on confirmation from specific manufacturers 
at this point on a per-card basis until I've had enough personal experience 
to reliably assume support or non-support.
Thanks again to everyone.
--
Shawn Wilson 

 fault tolerant system, 
Nonsense. That's just an application.
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 to reliably assume support or non-support.
Good approach. Run your NAS paralled to tape based backup procedures for a
while.
Don't forget to check hardware claimed reliability numbers. Last time I have
checked, RAID SATA cotrollers had relatively low numbers.
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 Which motherboard was that?
My personal motherboard is currently an MSI nForce2 board... although I'm at 
work and can't recall the model number.  It's DDR400, Athlon XP, 2 SATA 
ports, AGP 8x, dual NICs (one gigabit).  Google searches are making me think 
it's a KT4 Ultra, however today I'm getting much more information and it's 
quite prevelant that the onboard SATA supports RAID.  I don't remember mine 
being 'bluetooth ready' but it must be since this looks like my board.
I'm trying to decide on an upgrade path, but I'm holding off just a bit 
because I can't decide on PCIe vs AGP for my next video card.  My question 
there isn't about performance ceiling so you don't need to tell me about the 
glorious PCIe.  I've been keeping up on it and realize the potential for 
PCIe, but in my price range I can go either way and have the same 
performance.  My last thought was looking at an X800, but that's on a back 
burner and off topic.
--
Shawn Wilson

 then put in the swaps in order for it to work without issue.
I wonder how RAID controller would like to rebuild 3 drives at once? That
will be an interesting experiment...
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Just be careful using above NAS for system images and archived files. Make
sure you have a second copy of those handy...
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