How to operate becache
Recently I just try to add bcache with zfs and ceph. So I just wirte down it.
Since bcache implement in Linux kernel. So it will default enabled. We just need to install bcache-tools to operate bcache.
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| apt install -y bcache-tools
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| # make a cache disk for bcache .It must be a ssd disk.
make-bcache -C /dev/nvme1n1
# make a disk as backend disk.It must be a slow sata/sas disk.
make-bcache -B /dev/sda
#if you have a lot of disks like me.your can add backend disk as this.
make-bcache -B /dev/sd{a..f}
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###Check bcache status
Add bcache manually
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| #show `cset.uuid
root@xa-autotest-hci01:~# bcache-super-show /dev/sda
sb.magic ok
sb.first_sector 8 [match]
sb.csum ED8FD98E20A2E91E [match]
sb.version 1 [backing device]
dev.label (empty)
dev.uuid e7b350fe-3496-47e2-a276-5faa5637f8a5
dev.sectors_per_block 1
dev.sectors_per_bucket 1024
dev.data.first_sector 16
dev.data.cache_mode 1 [writeback]
dev.data.cache_state 1 [clean]
cset.uuid d3fcd781-a10a-453a-96dd-6eba13abfc5b
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####Add cache disk
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| echo "d3fcd781-a10a-453a-96dd-6eba13abfc5b" > /sys/block/bcache0/bcache/attach
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if you have a lot of disk, you can add it with for loop.
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| for i in range{0..5}; do `echo "d3fcd781-a10a-453a-96dd-6eba13abfc5b" > /sys/block/bcache$(expr $i)/bcache/attach`; done
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Delete cache disk
if you want to delete bcache disk
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| echo "d3fcd781-a10a-453a-96dd-6eba13abfc5b" > /sys/block/bcache0/bcache/detach
# delete a lot disk
for i in range{0..5}; do `echo "d3fcd781-a10a-453a-96dd-6eba13abfc5b" > /sys/block/bcache$(expr $i)/bcache/detach`; done
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unrigister cache disk
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| umount /dev/bcach0
echo 1 > /sys/block/bcache0/bcache/stop
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If you onle have one nvme disk and you can add them all in one
make-bcache -C /dev/nvme1n1 -B /dev/sd{a..f} –writeback
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## Change bcache write policy
```bash
make-bcache -B/dev/
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Manually resigter udev disk
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| echo /dev/sdb > /sys/fs/bcache/register
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Change bcache write mode
When you run command like make-bcache -C /dev/nvme1n1 -B /dev/sda it will be set write through mode. If you have UPS and you can change it to writeback mode.
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| echo writeback > /sys/block/bcache0/bcache/cache_mode
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Check bcache status
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| cat /sys/block/bcache0/bcache/state
no cache: this means you have not attached a caching device to your backing bcache device;
clean: this means everything is ok. The cache is clean;
dirty: this means everything is setup fine and that you have enabled writeback and that the cache is dirty;
inconsistent: you are in trouble because the backing device is not in sync with the caching device;
bcache-status
lsblk
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bcache optimized
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| #modify cache policy
cat /sys/block/bcache0/bcache/cache_mode
echo writeback > /sys/block/bcache0/bcache/cache_mode
#Disable ip track
echo 0 > /sys/fs/bcache/$CacheSetUUID/congested_read_threshold_us
echo 0 > /sys/fs/bcache/$CacheSetUUID/congested_write_threshold_us
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disable bcache
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| #check `CACHE_SET_UUID`
ls /sys/fs/bcache
#Unregister ssd cache disk
echo 1 >/sys/fs/bcache/06e33354-7c21-4c52-990d-1a653617ab20/unregister
#disable backend disk
echo 1 > /sys/block/sdb/bcache/stop
#write back cache to backend disk
echo 0 > /sys/block/bcache0/bcache/writeback_percent
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##Reference