Hello there. I'm not sure if this is the appropriate venue, so please
let me know if this information should be somewhere else. I have
configured a Debian 7.0 installation on a Dell Inspiron 17R SE laptop to
use a bcache root device. The previous known working configuration for
the laptop was:
/dev/sda (1TB HDD)
...
/dev/sda7 (used as LUKS encrypted volume)
/dev/mapper/sda7_crypt (used as LVM PV)
/dev/vg0/home
/dev/vg0/root
...
/dev/sda8 (used as ext3 /boot)
The new configuration is
/dev/sda (1TB HDD)
...
/dev/sda7 (used as bcache backing device)
/dev/bcache0 (used as LUKS encrypted volume)
/dev/mapper/bcache_crypt (used as LVM PV)
/dev/vg0/home
/dev/vg0/root
...
/dev/sda8 (used as ext3 /boot)
/dev/sdb (32GB SSD)
...
/dev/sdb3 (used as bcache caching device)
In order to get things booting, I also:
* Installed a Linux 3.10 kernel from wheezy-backports
(3.10-0.bpo.2-686-pae)
* Obtained a copy of the bcache-tools source from the git repo and
compiled it
* Constructed a Debian package for bcache-tools using checkinstall
* Because udev recognition wasn't enough at boot time, added a
script /etc/initramfs-tools/scripts/init-premount/z-bcache which looks
like this:
#!/bin/sh -e
# ZEP - Added (2013-08-29) because some bcache devices were
not being detected
# at startup by udev. This sloppy hack should do the
job.
PREREQS=""
prereqs() { echo "$PREREQS"; }
case "$1" in
prereqs)
prereqs
exit 0
;;
esac
. /scripts/functions
if [ -e '/sys/fs/bcache/register_quiet' ]; then
log_begin_msg "Scanning for bcache devices..."
for d in `ls /dev/sd*`; do
echo "$d" > /sys/fs/bcache/register_quiet
2>/dev/null || true
done
log_end_msg "bcache device scan complete"
else
log_warning_msg "/sys/fs/bcache/register_quiet not
found; not registering devices"
fi
* Executed update-initramfs -u -k all to get everything working
My machine boots from /dev/sda8 and the initramfs has enough machinery
to get the root drive mounted. I was thrilled until I discovered that
neither suspend nor hibernate seems to work; the suspend process seizes
up while suspending devices and never comes back. I booted the laptop
from a custom Debian live disk using the same kernel
(3.10-0.bpo.2-686-pae) and performed a series of tests:
* When the bcache kernel module was not loaded, suspend to RAM
worked correctly.
* When the bcache kernel module was loaded but no devices were
registered, suspend to RAM worked correctly.
* When a single bcache device was registered using "echo /dev/sda7
> /sys/fs/bcache/register; echo /dev/sdb3 > /sys/fs/bcache/register",
suspend to RAM failed to change the power state of the machine.
* With a /dev/bcache0 device in use as an encrypted volume, running
"echo freezer > /sys/power/pm_test; echo platform > /sys/power/disk;
echo disk > /sys/power/state" allows the machine to awaken from the test
correctly.
* With a /dev/bcache0 device in use as an encrypted volume, running
"echo devices > /sys/power/pm_test; echo platform > /sys/power/disk;
echo disk > /sys/power/state" causes the machine to hang.
Has suspend/hibernate been tested with bcache? Is it supported? I'm
trying to figure out if it's my specific laptop hardware causing the
issue or if bcache is somehow at fault. (Clearly, I can get
suspend/hibernate back if I migrate back to using just my HDD, but
caching blocks in a fashion designed for SSDs seems like such a lovely
idea.)
Thanks,
Zach
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