Geek corner: Hard drives / ‘mobile racks’ ?

Factual Questions
1

Which, it’ll come as a surprise to some, have nothing to do with breast implants.

I like the concept if it works as I think it does. What I’d like to do is confirm my understanding, and ask a couple more practical questions. So …:
It’s a system that allows you to (basically) ‘plug and play’ hard drives – you stick one of (what may be) several hard drives in the PC and that drive automatically becomes the primary / master. You then take that out, swap it for another as it suits and reboot … If that’s correct, it makes handling different O/S’s and having, say, e-mail separate from, say, development, a lot, lot easier. Also, you can take H/D’s to different locations. Finally, with the ‘hot summin’, you can move data across H/D’s easily (allegedly) …. Is all of that an approximation of what ‘mobile racks’ allow you to do ?

Plus:

The other thing I haven’t quite grasped is whether I need a new case – how do the racks themselves slot into the casing ?

Finally (while we’re here although I guess it’s more ‘IMHO), anyone any experiences of mobile racks they’d care to relate ?

2

They vary. Mostly they mount in a half height 5 1/4 inch bay, just the same as a CD or DVD drive.

“Cold swap” is what the cheapest ones do. Shut the machine down, swap one disk for another, restart with another operating system or whatever.

More expensive ones can “hot swap”, i.e. can be removed and replaced while the machine is still running, but I’ve never actually used one of those.

3

Use em, love em, LINUX on one Windows on others, works great!

4

So it really is ‘plug and play’ for hard drives … very handy.

Of course, the spare CD bays … I’ve got two left so that’s great.

Thanks guys

Anyone think of anything else I need to know ?

5

** Desmostylus**’ points are important. If the documentation doesn’t specifically say that the rack is hot-swappable, assume it isn’t. Power off your PC before inserting or removing the drive. Otherwise you risk killing your power supply.

If it has a lock on the front you will probably need to turn the key after inserting the drive (but before turning the power on) in order to activate it. The instructions don’t always make this clear.

Try to find a rack that has a spring-loaded door which shuts when the drive isn’t in. This prevents (as much) dust from getting in and also looks much better than a gaping hole in your case.

A removable hard drive is great for running full backups of home PCs. It compares very favorably with CD-Rs and tapes in terms of speed and capacity.

6

if the drive is the ‘system drive’ (the one with the OS installed) you can only use it on another computer if the hardware is (mostly) the SAME. and even then there could be some weirdness.

you should be able to mount it as a secondary drive on almost any machine.

7

Another aspect of mobile racks relates to something called RAID (redundant array of independent disks). At its most basic level, you have two drives that act as one. So when data is copied to drive 1, it is also copies to drive 2.

This is handy, because if drive 1 were to ever crash, you’d have an exact copy on drive 2, right down to the last piece of data that was copied. It is unlikely that they’ll crash simultaneously.

8

Hmmm… replace “copied” with “written”.

9

How do they relate? :confused:

You can have mobile HDDs without using RAID, and vice versa.

10

Hot swap RAID can be very useful on a server. A redundant disk dies, so you just rip it out and replace it without having to shut down the server. The RAID software then copies all of the data from the surviving disk onto the new disk. Example.

11

Okay, I’ve taken on board Desmostylus point about cold vs. ‘hot swapping’ – I’m assuming that’s a software issue rather than anything to do with the drive itself but I’ll get that confirmed by the dealer.

Number, I like your points about dust and backups – both very good . Thanks.

If anyone’s still around, I have two supplemental:
This I don’t get:

See, I understand that in the context of a machine with two drives working as primary and secondary. Here though, we’re talking about a different deal all together, I thought - i.e. each drive is wholly independent and with its own O/S installed …. Is that not the case ?
Finally, I don’t know about RAID but could it also be utilised as an ongoing ‘real-time’ data back up system (written or downloaded) ? Maybe my understanding is off ?

12

Whoa.

  1. Hot vs cold swapping isn’t just a software thing. As number pointed out, you have to be careful about this. If the system isn’t designed for hot swapping, you risk damaging the system if you pull the disk out.

  2. da_pope is telling you about a slightly different situation. If the removable disk is the “system disk”, the one that the machine boots from, then you can’t easily boot a different machine from the same disk, because the operating system will try to load software drivers for bits of hardware that aren’t there, or don’t match.

  3. RAID (some versions) is in fact a “real time” data back up system. That’s exactly what it’s for.

13

Okay Desmostylus, I need to make sure (from the manufacturers docs) that the rack itself is ‘hot-swappable’ … thanks

I think I get this, an example: If I buy, say, a new cordless keyboard and install the relevant software on Drive A but then I take out Drive A and slot in Drive B - where the keyboard software hasn’t been installed - I need to install that same software on Drive B for it to work ? Sure.

Same situation if I take Drive A to a friends computer – I’d also need to install the keyboard software (or maybe, as an alternative, take my keyboard itself along !?)

  • so what we’re talking about is software drivers for hardware components…Please tell me that’s the point da_pope is making ??
14

Wait. We’re getting stuck in shuffling hardware without considering the OS.

You can get snap in bays that allow you to insert & remove drives from a PC. Here’s one.

The master/slave setting for the drive is set on the drive itself, usually via jumper on a couple of pins. There’s also a new gizmo that’ll let you switch the master/slave pins to swap between two drives.

The hot-swap/cold swap from a hardware point of view is usually just a matter of pins for the powering of the drives. What’s more important is just how your OS is going to behave if all of a sudden one drive goes away and another arrives. Most likely, Windows will misbehave in this situation.

If you really want a portable drive you can carry between computers, I suggest you get one of the USB 2.0 varieties that are designed for just this purpose. You can plug and unplug it and the OS should react just fine.

If you’re looking for RAID drives, allowing hot-swap for failed drives in a RAID-5 or mirror situation, I suggest looking at the cards from Promise Technology, but they’re a little beyond common home usage.

15

Basically, yes, but keep in mind that the even the most basic components (CPU, motherboard, etc.) have software/configurations that are stored in the OS. So the more the two machines differ, the more impossible it becomes to just pop the OS drive into that second machine. Windows 98, in my experience, is fairly tolerant of redetecting hardware in different machines, and after a reboot or two, usually works ok. Windows NT/2000/XP would be much more difficult to do this with (XP would break activation even if it did work). It should be possible to make Linux work well on differing hardware, as long as the kernel is not customized.

Basically, I think you need to consider Belrix’ point. What you need depends on whether you would like to be able to use multiple OS’ or be able to transfer data easily between different machines.

16

Maybe I can make my point clearer:

You own machine A, it’s a Dell Pentium 4 - 2Ghz, ATI card, and Intel motherboard. You set up a removable drive bay, load a Maxtor 40GB hard drive in the tray, set as master on the primary IDE chain.

You set up windows XP, do all the patches and service packs, Office, and other programs, everything works swell.

Your friend owns machine B, a HP AthlonXP 2000, Nvidia card, AMD motherboard. You install a removable drive bay in this machine and bring your tray with the Maxtor 40GB over, with the intention of booting the machine with your copy of windows XP.

Put the drive in, turn the key lock, push the power button and viola!! BSOD (blue screen of death). Why? Well, in the case of NT, (or 2K or XP) it’s the IDE driver. The one installed for your Intel motherboard won’t have a chance in hell on the AMD VIA IDE chipset. And so it goes down the line, if it wasn’t the chipset it woulda been the video drivers, the motherboard resources etc…

Now, say you have machine A, you have the OS installed on an internal 40GB Maxtor HDD set as the master on your primary IDE chain, and install the removable bay as the slave on your primary chain. You mount a Seagate 80GB in the removable tray and slide it into your new bay. You store all your MP3s and videos and other data type files on the removable drive (probably shows up as ‘D’ in windows explorer) with the intention of bringing it over to your buddies. Slide the tray out; mosey over to your friend with the HP machine. Install a removable drive bay on his machine as the slave on the primary chain, or even the slave on the secondary IDE chain, slide the drive tray in and power up. As long as his BIOS is set to auto detect (and most newer machines are), you should find a new drive in windows explorer, with all your fun stuff on it.

Now, there are a few caveats:

As said above, windows 9x (95,98,Me) can sometimes be more tolerant of odd hardware all of a sudden appearing, so you can be successful sharing one system drive between 2 hardware boxes. I wouldn’t count on it reliably though.

If machine A is XP (or NT or 2K) the drive is probably formatted using a file system called ‘NTFS’, which any 9x (95,98,Me) system will not be able to read. So even if it’s a secondary drive in machine A and you pop it in as a secondary on machine B, and machine B is 98, windows is going to claim the drive is not formatted, would you like to format now? You need to say NO; otherwise you’re going to completely erase the contents of that drive. Going the other way will work though. If machine A is 98 and you pop out that secondary drive (which is most likely formatted as ‘FAT32’) to put in machine B, which is XP, It should read the drive no problem. XP can read NTFS, FAT16 and FAT32.

If you have programs on your removable drive, don’t count on them to run properly when you put the drive in machine B. There is usually stuff installed on the system drive that the programs you installed on the removable depend on. Might work, might not.

Your best bets for removable drives is either:

  1. One bay mounted in one machine, two trays, a unique OS on each.

  2. 2 bays mounted as ‘slave’ or secondary’ drive positions in different machines, with the intention of ONLY sharing data type files. (Watch out for compatible file systems)

good luck!

17

I’ve heard RAID defined where ‘independent’ is replaced by ‘inexpensive’, and sometimes ‘identical’. I’m sure I’ve heard ‘disks’ replaced with ‘devices’, too … a redundant array of independent/inexpensive/identical discs/devices. IYSWIM.

I think the ‘inexpensive’ version came first. Not sure though.

Not always - this depends on the way the RAID is set up. For example, in RAID 0 there’s no redundancy, data is striped across the multiple discs. This increases read and write speed, and gives you access to all your disc space[1], but gives no data backup. In RAID 1 (‘mirroring’) for a pair of discs, one of the discs is simply a copy of the other (as stated above). More fancy versions exist, with various flavours of backup / data protection / funkiness.

BfT.

[1] Well, twice the amount of space on your smaller drive, as it 'appens.