Question Thunderbolt drive performance issue

[Permeus]

Hi everyone. I recently reported a crash issue with my external TB drive to which there appears to be no solution so far (see "Thunderbolt boot drive crashes after wake from sleep" thread for details). I have since discovered another interesting problem related to the same drive when using it on my new Dynabook A50-J: Write performance suffers considerably when transferring files to the TB drive when the laptop is booted from the internal drive. When booting the same OS from the TB drive, however, peformance returns to normal, curiously enough. A couple of screenshots from HD Tune demonstrate the situation:

Write performance when booted from internal drive:

Write performance when booted from TB drive:

The performance figures are backed by real-world file tranfer speeds to the TB drive which are 130-150 MB/s when the OS is booted from the TB drive and drop to a meager 13-15 MB/s when the system is booted from the internal drive.

Dynabook's web site has changed since I contacted them about the crash issue and there's no longer a page to send them a support request. Their live support link is defunct at this time (https://dynachat.fix4pc.com/). Two community forums are listed (https://support.dynabook.com/forums), Microsoft and Tom's Hardware, which is why I decided to post about this problem here.

Any info on fixing the drive performance issue would be highly appreciated.

Cheers.

 

[sbgardne]

Since you mentioned your Dynabook is new, I'd check the Dynabook "Drivers and Software" link, enter your model or serial number, and ensure that you've got the most recent manufacturer updates. I've recently resolved two separate Thunderbolt performance issues by updating drivers and firmware.

HTH

 

[Permeus]

Updating drivers when new ones become available is, of course, always recommendable. This is not a driver version issue however, since I ran exact copies of the original OEM OS on either drive for testing. In both instances the exact same drivers are used, yet the drop in performance only occurs when booting from the internal SSD. I rather suspect this to be related to how Windows handles the external TB drive, more specifically the file system it's writing to, in either case. The X5 TB SSD is an AF drive with 4k sector size, compared to 512 for the internal drive, which could be related to this issue. I'll run a Windows Update on the factory OS image and see what that produces.

Cheers.

 

[Permeus]

As I suspected, the problem lay in the way Windows handles the TB drive when it boots from the internal one. The internal drive has a sector size of 512 bytes, so Windows essentially runs in 512-byte mode, requiring the file system on the TB drive to be 4k-aligned. Otherwise it performs a couple of extra read-modify-write operations for each sector it's writing to, drastically reducing write performance. The partition on the TB drive I've been using for testing was formatted by the imaging software I used, which employs a Windows 8.1 or older formatting routine. Re-formatting the partition under Windows 10 resolved the problem and the OS is able to write to the partition at full speed. Here are the details:

TB drive file system formatted by imaging software:

As we can glean from this info, the MFT of this file system starts at an offset of 0x80, or 128 bytes in decimal. This number is not divisible by 4096 bytes and the file system is therefore not 4k-aligned.

TB drive file system formatted by Windows 10:

The MFT of this file system starts at an offset of 0xc0000, or 786,432 bytes in decimal. This number is divisible by 4096 and yields an offset of exactly 192 sectors. The file system is therefore 4k-aligned.

PS Running Windows Update had no effect in resolving this issue.

 

[Permeus]

As I suspected, the problem lay in the way Windows handles the TB drive when it boots from the internal one. The internal drive has a sector size of 512 bytes, so Windows essentially runs in 512-byte mode, requiring the file system on the TB drive to be 4k-aligned. Otherwise it performs a couple of extra read-modify-write operations for each sector it's writing to, drastically reducing write performance. The partition on the TB drive I've been using for testing was formatted by the imaging software I used, which employs a Windows 8.1 or older formatting routine. Re-formatting the partition under Windows 10 resolved the problem and the OS is able to write to the partition at full speed. Here are the details:

TB drive file system formatted by imaging software:

As we can glean from this info, the MFT of this file system starts at an offset of 0x80, or 128 bytes in decimal. This number is not divisible by 4096 bytes and the file system is therefore not 4k-aligned.

TB drive file system formatted by Windows 10:

The MFT of this file system starts at an offset of 0xc0000, or 786,432 bytes in decimal. This number is divisible by 4096 and yields an offset of exactly 192 sectors. The file system is therefore 4k-aligned.

PS Running Windows Update had no effect in resolving this issue.

Ok, so it turns out that the MFT start LCN is not a byte offset but rather the index number of the LCN, which would make the file system in both instances 4k-aligned. In other words I have no explanation for the drastic drop in write performance with the first volume, but there it is - when booting from the internal 512b-sector drive, performance drops, yet the same file system performs optimally when booting from the external 4k drive. Curious.