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Sipos
Tux's lil' helper
Tux's lil' helper


Joined: 10 Sep 2004
Posts: 107
Location: London

PostPosted: Fri Nov 23, 2012 11:35 pm    Post subject: Kernel messages with external hard drives Reply with quote

Hi,
I've got 4 new 3TB harddrives in an external enclosure with a JMicron USB SATA controller. When I connect it to the system there are a couple of messages for the disks in dmesg that I don't understand. They are

Code:
sd 0:0:0:0: [sda] Very big device. Trying to use READ CAPACITY(16).


and

Code:
sd 0:0:0:0: [sda] No Caching mode page present


Does anyone have any idea what the first message means and, does anyone know if the second one means that the disk cache isn't working properly or, how I can check? Any help would be much appreciated.
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VinzC
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Joined: 17 Apr 2004
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PostPosted: Sun Nov 25, 2012 11:57 am    Post subject: Reply with quote

Have you formatted your drive with GPT?
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NeddySeagoon
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Joined: 05 Jul 2003
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PostPosted: Sun Nov 25, 2012 2:40 pm    Post subject: Reply with quote

Sipos,

I've seen that with a 1Tb USB2 HDD.

It goes on to be quite scary. fdisk -l reports the wrong size and partitions are missing from the partition table. The partition table signature is missing and testdisk can read well over 1Tb from the drive. For me, its only started happening if the USB drive is connected at boot. The workaround is to unplug the USB lead, allow the drive to spin down, then reconnect the USB lead.
Reconnecting the USB lead before the head parking click is heard just repeats the same incorrect drive detection.

I don't have a real fix.
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Sipos
Tux's lil' helper
Tux's lil' helper


Joined: 10 Sep 2004
Posts: 107
Location: London

PostPosted: Wed Nov 28, 2012 12:58 pm    Post subject: Reply with quote

Thanks for your replies.

Quote:
Have you formatted your drive with GPT?


No, at the time of my original post, I hadn't formatted the disk at all yet. I have now.

Quote:
It goes on to be quite scary. fdisk -l reports the wrong size and partitions are missing from the partition table. The partition table signature is missing and testdisk can read well over 1Tb from the drive. For me, its only started happening if the USB drive is connected at boot. The workaround is to unplug the USB lead, allow the drive to spin down, then reconnect the USB lead.
Reconnecting the USB lead before the head parking click is heard just repeats the same incorrect drive detection.


fdisk seems to detect all the correct information for me. I've now partitioned the drive (using GPT) to create a single large (3TB) primary partition with parted and created an ext3 filesystem on it. I can read and write to it (at least I haven't encountered any problems with limited testing). I haven't seen any similar problems thankfully.

It does take a long time to mount the filesystem. I'm not sure if the time to mount increases significantly with size but, it takes 3 minutes to mount it which seems like a very long time.

I have done some googling, reading etc and, I think the there is a SCSI command READ CAPACITY that comes in two formats: 10 or 16 bytes. The maximum size disk for which the 10 byte command works is 2.2TB so, for larger disks the kernel has to issue a 16 byte READ CAPACITY command. I think this message appears in the log to warn that the kernel is using the READ CAPCITY(16) command because some controllers do not support it and provide inaccurate information back. This is what the 'Very big device. Trying to use READ CAPACITY(16).' message is about. I guess this is only an issue when the actual device is a real SCSI device, not a SATA device since, for SATA devices, the SCSI commands are being translated to ATA commands by the kernel.

The 'No Caching mode page present' message is followed by 'Assuming drive cache: write through' so, apparently the kernel isn't able to detect the disk cache. This does seem to be a problem to me since the disk is hard disk and does have a cache. I can't find any information online about it other than a forum post about someone else having the same trouble but, no answer to what they did. I'm not sure if there is anywhere else I can ask really.
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