Backup devices - idea

[bronto]

Thanks Tim;

It sounds like my idea is a little bit ahead of it's time.  Glad I didn't 
but the stuff when I was shopping today.

Rob


At 02:21 PM 6/1/02 -0700, you wrote:
>At 12:13 PM -0700 6/1/02, bronto wrote:
>>Here's an idea - maybe someone with experience can comment on it.
>>
>>I'm thinking I may be able to get the best of all worlds by using
>>removable/swapable hard drives as my media.  They're fast, reusable,
>>large capacity, and relatively cheap.  According to my inquiries, about
>>as cheap per gigabyte as tapes, so I could even archive them and not
>>re-use them if I were so inclined.  My questions are: 1) Reliability -
>>in theory if treated with respect they should be as reliable as
>>permanently installed HD's, but is that realistic,
>
>You will need to treat them with a lot of respect.  One of the major 
>reliability problems for hard drives is improper handling leading to 
>eventual failure.  Definitely a lot more susceptible to physical impact 
>than tapes.
>
>>2) will they be
>>hot-swappable in linux?  Will I have to manually mount the drive
>>everytime they are rotated (daily)?  I know they don't have to be on
>>Windows or Mac, but Linux? and
>
>The major problem is hardware support for hotswap, the secondary problem 
>software support.  If you plan on using IDE drives and a built-in IDE 
>controller, think again.  IDE is not designed to hot swap and you can kill 
>drives trying to do so.  Furthermore, last time I researched the topic, 
>the Linux kernel has no concept of IDE drives going away and coming back.
>
>(Some of the removable IDE drive carrier kits claim to provide safe 
>hotswap capability, and they may well do so, but the kernel still won't 
>know how to handle it.)
>
>SCSI, on the other hand, has officially defined ways for devices and host 
>adapters to support hot swap.  These days, almost any Ultra 160 SCSI drive 
>and/or HA probably has hotswap support (but read docs to be sure; most 
>SCSI HDs have extensive technical manuals that can be found on the mfr's 
>web site if you dig enough).  The kernel supports rescanning SCSI IDs and 
>there is a script out there which automates rescanning all SCSI busses 
>(search for rescan-scsi-bus.sh on Google). This will be a lot more 
>expensive than you were anticipating however.
>
>The third way (that I know of) which solves both the hardware problem and 
>the software problem is to use FireWire.  FireWire is hotswappable by 
>design, of course.  The trick on the software side is that FireWire 
>storage devices look like SCSI to Linux, even if they're really IDE in the 
>end.  (The FireWire storage device protocol is nothing more than a way of 
>using FireWire as a transport for SCSI commands, so it really is a form of 
>SCSI.)  The IDE-to-FireWire boards used to create FireWire hard drives 
>handle the job of translating commands and results between the SCSI domain 
>and the IDE hard disk drive.
>
>So, your setup would be a removable hard drive frame in a 5.25" external 
>FireWire case.  To swap out a drive, you would:
>
>1. Unmount it
>2. Unplug the FireWire cable
>3. Power down the external drive case
>4. Remove the HD
>5. Put in a new one
>6. Power up the case
>7. Plug the FW cable in
>8. Rescan the "SCSI" bus
>9. Mount the drive
>
>(optionally, after (1) perform a SCSI bus rescan to let the kernel know 
>that the drive was removed).
>
>>3) Compatibility - will using these drives throw a curve ball at
>>standard backup utilities?
>
>That would depend on the utility you use, I would guess.
>--
>Tim Seufert
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