Hot Swap and Smart Hot Swap - How To :

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Hot Swap and Smart Hot Swap - How To :

Postby Spildit » Sun Dec 08, 2013 5:13 pm

Hot Swap Method :

Fixing a hard drive’s firmware is quite straightforward: just locate the corrupted modules in the System Area and fix them. However, what if the drive cannot write to the System Area to fix corrupted modules? There is still a way around this problem: a method called Hot Swap.

Firmware corruption on modern hard drives usually occurs when one or more modules are damaged in the System Area on the disk platters. Fixing this type of problem requires specialized utilities to test and repair corrupted modules. Usually, the repair can be done using PC3000 on the fly, and it doesn't require any extra steps to perform.

Sometimes, however, some modules can’t be fixed. This could be due to the following reasons:

-There is media damage in the System Area, so heads cannot write in that area.
-There is some damage to system heads write elements, so heads cannot write at all.
- Modules containing unique write parameters for the heads (adaptives) are corrupted, so the drive cannot write.
-The hard drive doesn't give access to System Area if some critical modules are corrupted.

If some modules can’t be fixed, the solution is to use the Hot Swap method to access the drive System Area and try to repair the modules.

A Hot Swap procedure generally follows these steps:

1. Use a matching donor drive, enter the specialized utility, and make sure that the drive is in working condition.
2. Put the donor drive into Standby mode using a special command from within the utility. This command makes the drive spin down the motor without cutting power to the drive.
3. Carefully hot-swap the board by disconnecting it from the good donor drive and connecting it to the bad drive. Even though the drive is not spinning, the board is still alive.
4. Wake up the drive by executing Recalibrate or another ATA command; if the donor drive was compatible enough, the bad patient drive should spin up and become ready.
5. Test the System Area and repair corrupted modules as needed.

So, the idea is essentially to initialize a donor PCB with firmware from the donor drive, then hot-swap the board to the faulty hard drive and repair corrupted modules.

This procedure can usually be applied for cases c) and d). Unfortunately, when there is a hardware problem with heads (b) or media (a), hot swapping won't allow you to repair corrupted modules. For these complex cases, there is a Smart Hot Swap method to use, which we will explain in another post.

Smart Hot Swap Method :

The Smart Hot Swap method for recovering data from drives with complex damage is based on the basic Hot Swap technique explained in our earlier post.

The Smart Hot Swap procedure is very important in modern hard drive recoveries. In some situations it is the only way to get access to user data, and without mastering this method, a certain percentage of cases will remain unrecoverable.

A basic Hot Swap often allows technicians to access the hard drive system area and repair corrupted modules. However, sometimes the basic method isn’t enough, as in these cases:

a.There is media damage in the System Area and the heads cannot write in that area, so modules cannot be repaired.
b.There is some damage to the system heads write elements, so the heads cannot write at all.
c. One of the heads is bad, the hard drive is clicking, and you want to at least image sectors that belong to the good heads before swapping heads from the donor.

In those cases, a basic Hot Swap won't allow you to repair the drive and have it start up on its own. Instead, you can use a Hot Swap to jumpstart the drive and try to image the user data rather than repairing the firmware.

The limitations of a basic Hot Swap for imaging

Obviously, every hard drive is different, and if you just try to read data on the damaged patient drive after a basic Hot Swap without preparing the donor drive first, various things could happen:

a.The drive may start clicking as soon as you start accessing the data.
b. Every single read attempt may return an error or just time out.
c. Sectors may seem to read fine but afterwards you may encounter shifts in data, such as missing or redundant sectors, that may result in an inability to recover the file system.
d. The drive could read fine up to some point and then error out on every sector after a certain LBA (Logical Block Addressing) number.

All of these problems are caused by the simple fact that the firmware modules on the donor and patient drives are not compatible. In cases a) and b), most likely the adaptives are not close enough, and in cases c) and d) the translator tables are different, so after being initialized with the donor translator, the drive seeks for the data in the wrong place on the patient drive.

The Smart Hot Swap method gets around these limitations.

How to do a Smart Hot Swap and get more data

For a Smart Hot Swap, you prepare a donor drive that is identical to the bad drive firmware-wise and then use that donor for a Hot Swap to read the data from the bad drive without fixing it.

Here's the procedure for a Smart Hot Swap:

1.Read all System Area (SA) tracks from the patient drive. If you can't read all of the System Area tracks for some reason, you may need to employ the Hot Swap method.
2.Prepare your Smart Hot Swap donor drive by writing all of the patient SA tracks. This step makes your donor System Area fully identical to the one on your patient drive so that all defect lists, adaptives, and other modules are in sync with the patient drive.
3.Once the Smart Hot Swap donor is ready, you can put the patient PCB on your donor, start it up, make sure it IDs with the patient S/N, perform a Hot Swap and start imaging the data.

The procedure above is simplified, and in some cases you may need to modify it or add some extra steps. For example, copying firmware by SA tracks works well on Western Digital and Samsung, while on Maxtor and Seagate it does not, and you will need to transfer only specific translator/adaptive firmware modules from patient to donor. On some newer Western Digital hard drives, some unique adaptives are stored on the PCB board in ROM, so you may need to tweak these parameters in the patient ROM to make the board start on the donor drive, for example. All of these little details are well covered in our training classes, forums, and the PC3000 manuals.

Another thing to keep in mind is choosing the right donor for a Smart Hot Swap. These rules vary from vendor to vendor but the general rule “The closer – the better” usually applies. Quite often, however, you may need to consider some other internal parameters that you can’t find on the drive’s label, such as head map configuration, adaptives compatibility, and matching firmware revision.
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Re: Hot Swap and Smart Hot Swap - How To :

Postby wayne_horner » Wed Mar 25, 2015 12:54 am

if the sa has bad sectors that are mapped out then doesnt that make the smart hot swap method of writing all the tracks a problem?

if the donor has 3 sa sectors mapped out
then if your transfer all the tracks from the patient to the donor
then you are trying to overwrite sectors which are bad and mapped out

so wouldnt that be a problem?

Or usually its not critical so it still works?

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