Data recovery adapter designed with wrong chip - Page 1
Forum section: electronics / general

author: fzabkar
author_rank: Super Contributor
timestamp: October 26, 2019, 06:51:34 am
content: Several HDD manufacturers integrate the USB-SATA bridge IC into the HDD PCB in many of their external storage products. Normally the bridge would be on a separate board. This poses a problem for data recovery shops who need to access the drive via SATA.The solution is to replace the PCB with a SATA version, or to convert the USB PCB to SATA by intercepting the SATA Tx/Rx differential pairs running between the bridge IC and the HDD MCU. These four signals are then wired to the SATA host controller.This adapter is meant to facilitate the wiring:https://forum.hddguru.com/viewtopic.php?t=36261&start=20The signal lines would ideally be buffered by a SATA redriver IC with the appropriate characteristic impedance. Unfortunately the designer has chosen a 4-Channel High-Performance Differential Switch. This IC provides no buffering or impedance matching of any kind. It is simply an analogue switch. Worse still, this switch is permanently closed. This means that the IC is nothing more than a placebo -- it does nothing other than consume power and occupy real estate.

author: george.r
author_rank: Contributor
timestamp: December 02, 2019, 07:24:55 am
content: And here I thought I was foolish for always just having stripped one end of a SATA cable, tinning and grafting it onto the differential pairs, and epoxying that on for mechanical resistance. Sometimes drilling the PCB if no testpoints available on the exposed side.I wonder if they even read the datasheet for that switch.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 02, 2019, 01:25:44 pm
content: Doesn't UAS allow low level access over USB?

author: Yansi
author_rank: Super Contributor
timestamp: December 02, 2019, 01:52:19 pm
content: USB drives work through USB-MSC class, don't they? That allows a direct read/write of any sector, doesn't it? Where is the problem with the USB then? Can someone please enlighten me?//EDIT: Typo.

author: george.r
author_rank: Contributor
timestamp: December 04, 2019, 06:15:26 am
content: Quote from: Yansi on December 02, 2019, 01:52:19 pm1- Yes2- Ehm, sorta3/4- Direct access to the gubbins of the drive, e.g. tools like the PC-3000, when the Service Area is borked, or some other issue prevents the HDD from initializing and you gotta work thru the SATA interface and not the serial console. Or, alternatively, when the USB port has been ripped out, or the USB bridge chip otherwise damaged.

author: fzabkar
author_rank: Super Contributor
timestamp: December 05, 2019, 06:26:49 am
content: Data recovery tools require access to firmware modules which are often damaged when they are updated by a failing head. For example, the SMART data and defect lists exist in a hidden System Area (SA) on the platters and are particularly vulnerable to corruption. Access to the SA is via undocumented Vendor Specific Commands. There is no SCSI equivalent for these commands, so they need to be transmitted via ATA passthrough. This is more convoluted than direct SATA access.Furthermore, when a drive becomes unresponsive, it needs to be reset or power cycled. This is best done via SATA. The USB bridge interferes with command timeouts, among other things.Perhaps this primer will shed some light on how the firmware works.The hard drive -- a computer-within-a-computer:http://www.hddoracle.com/viewtopic.php?f=56&t=2600