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I have a smart TV (LG C1) that can "pause" live TV, but demands a USB HDD attached.

It will refuse a brand new USB 3.2 flash drive, but will happily use a 2014 mediocre HDD on USB 3.0. I have no idea why the TV explicitly requires a HDD instead of relying on the speed measurements it does anyway.

AFAIK, both devices are seen as mass storage. Is there some mechanism the TV uses to tell HDDs from flash drives, or did is it more likely I got a flash drive with poor performance?

Edit: The flash drive is 128 GB and the HDD is 1 TB. The manual says one must use a USB hard drive with at least 80 GB storage. The flash drive is FAT, the HDD has FAT and NTFS - only the FAT partition is seen. Oddly enough, the USB stick is fine for 'offline' TV recording (where pause/rewind is not done during recording) and playback.

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    \$\begingroup\$ How big is the new drive and does the TV support it? But this is a product usage question really for Samsung support. \$\endgroup\$
    – Justme
    Commented Jan 6, 2022 at 12:20
  • \$\begingroup\$ When you say “explicitly”, what does it actually say? Also I suppose the drive is formatted with a regular FAT file system? \$\endgroup\$
    – jcaron
    Commented Jan 6, 2022 at 13:22
  • \$\begingroup\$ The flash drive is 128GB, the HDD is 1TB. The manual says one must use a USB harddrive with at least 80GB storage. The flash drive is FAT, the HDD has FAT and NTFS - only the FAT partition is seen. \$\endgroup\$
    – Makotanist
    Commented Jan 6, 2022 at 15:36
  • \$\begingroup\$ If you put a video file on the flash drive, are you able to play it using the TV’s media player? In other words, is the limitation only related to live control, or does the TV not recognise it at all? \$\endgroup\$
    – jcaron
    Commented Jan 7, 2022 at 11:12
  • \$\begingroup\$ Please edit new information into your question, don't post it in comments. Otherwise, readers have to piece together the full scattered question. Thanks. \$\endgroup\$
    – TonyM
    Commented Jan 7, 2022 at 12:21

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As can be seen in this Microchip app note (Page 6, Table 4: "bInterfaceSubClass POSSIBLE VALUES"), the interface descriptor contains a field that differs between flash devices ("Reduced Block Commands (RBC)") and hard drives, which would use "SCSI transparent command set".

There might be other differences but interface limitations would be a primary candidate why a device would reject flash devices over hard disks.

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  • \$\begingroup\$ I was about to accept this, when I decided to actually check. Suprise, the flash stick is also bInterfaceSubClass 6 SCSI. In fact, the only fields different besides obvious things like vendor id are bcdUsb (3.2 vs 3.0), bEndpointAddress (normal, i think), and bMaxBurst (1 and 15 vs 7 and 7). Any theories? \$\endgroup\$
    – Makotanist
    Commented Jan 7, 2022 at 10:49
  • \$\begingroup\$ @Makotanist That's interesting, all my USB flash drives are RBC. Highly likely that the SCSI protocol itself allows for yet more querying of device capabilities but I have no experience there. \$\endgroup\$
    – Unimportant
    Commented Jan 7, 2022 at 11:06
  • \$\begingroup\$ There’s some way to check if the device supports/needs TRIM (which is specific to SSDs, not sure if it’s supported in run if the mill USB flash drives, though), I believe via the ATA IDENTIFY DEVICE command. There may be other relevant fields in there. \$\endgroup\$
    – jcaron
    Commented Jan 7, 2022 at 12:33

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