Arch Linux

toni

Member

Registered: 2011-10-15

Posts: 437

No caching mode page present / Assuming drive cache:write through

I have arch linux installed in an external hard disk which is placed into an enclosure usb 3.0. External disk is attached to laptop through USB 3.0.
When booting some weird information appear:

[    2.366666] scsi 6:0:0:0: Direct-Access     FUJITSU  MHV2160BT        0000 PQ: 0 ANSI: 5
[    2.366666] sd 6:0:0:0: [sdb] 312581808 512-byte logical blocks: (160 GB/149 GiB)
[    2.366666] sd 6:0:0:0: [sdb] Write Protect is off
[    2.366666] sd 6:0:0:0: [sdb] Mode Sense: 23 00 00 00
[    2.366666] sd 6:0:0:0: [sdb] No Caching mode page present
[    2.366666] sd 6:0:0:0: [sdb] Assuming drive cache: write through
[    2.369999] sd 6:0:0:0: [sdb] No Caching mode page present
[    2.369999] sd 6:0:0:0: [sdb] Assuming drive cache: write through
[    2.519999]  sdb: sdb3 < sdb5 sdb6 sdb7 sdb8 sdb9 sdb10 sdb11 >
[    2.519999] sd 6:0:0:0: [sdb] No Caching mode page present
[    2.519999] sd 6:0:0:0: [sdb] Assuming drive cache: write through
[    2.523333] sd 6:0:0:0: [sdb] Attached SCSI disk

As I understand, “No Caching mode page present” means that the kernel wasn’t able to detect the cache available on the disk.
By the other hand, “Assuming drive cache: write through” means that the kernel is assuming that there is no write cache.

I am a little worried about it as in case of a power failure for example, could the drive be left in an inconsistent state?

External hard disk consist on an entire extended partition which has the following logical partitions:

/dev/sdb5 -> boot
/dev/sdb6 -> tmp
/dev/sdb7 -> var
/dev/sdb8 -> root
/dev/sdb9 -> usr
/dev/sdb10 -> home
/dev/sdb11 -> swap

I am curious to know how to solve it. Anyway arch works ok, no problems.

Thanks.

Spider.007

Member

Registered: 2004-06-20

Posts: 1,175

Re: No caching mode page present / Assuming drive cache:write through

Google says: http://askubuntu.com/questions/167343/w … ed-warning

Hard disks have a small amount of RAM cache to speed up write operations. The system can write a chunk of data to the disk cache without actually waiting for it to be written to the disk. This is sometimes called "write-back" mode.
If there is no cache on the disk, data is directly written to it in "write-through" mode.

The Asking for cache data failed warning usually occurs with devices such as USB flash drives, USB card readers, etc. which present themselves as SCSI devices to the system (sdX), but have no cache.
The system asks the device: "Do you have a cache?" and gets no response. So it assumes there is no cache and puts it in "write-through" mode.

BillCosby

Member

Registered: 2013-05-03

Posts: 5

Re: No caching mode page present / Assuming drive cache:write through

I have the same problem, I have a hard disk connected to my PC via USB 3.0, it used to be connected via eSATA and the write cache worked, so evidently my disk has a write cache.

I experience the occasional micro-hang in some applications if the disk is accessed, so I really would like to use the write cache. Is there any way to tell the kernel to use a write cache for this disk? Or this is an USB thing, which makes it impossible to use it?