bcache_status.md

Bcache

Bcache technology allows to speed up the access (read and write) for slow devices. The idea consists on using a fast device (e.g., SSD) as caching device.

(slow hard disk)   (faster device, SSD)
    /dev/sda            /dev/sdb
      |                     |
[Backing device]    [Caching device]  <-- Actually, this is is set of caching devices (Caching Set)
      |                     |
      |__________ __________|                   
                 |
              [Bcache]
           /dev/bcache0

Bcache without Caching Device

If you are thinking about using bcache later, it is recommended to setup all your slow devices as bcache backing devices without a cache, and you can choose to add a caching device later.

(slow hard disk)   
    /dev/sda            
      |                     
[Backing device]    
      |                     
      |__________ __________|                   
                 |
              [Bcache]
           /dev/bcache0

Flash-only Bcache

A Flash-only Bcache is an special type of bcache. It has no backing device, and it is directly created over a caching set.

                   (faster device, SSD)
                        /dev/sdb
                            |
                    [Caching device]
                            |
      |__________ __________|                   
                 |
         [Flash-only Bcache]  <-- (WIP, seems that supports thin-provisioning)
           /dev/bcache0

YaST Status before this sprint

Supported by libstorage-ng

• Probe Bcache devices (with and without caching device)
• Create Bcache devices (with and without caching device)
• Delete Bcache devices

Supported by Expert Partitioner

• Show Bcache devices witho and without caching device
• Create/delete Bcache with caching device

Pending in libstorage-ng

• Probe Flash-only Bcache
• Create/Delete Flash-only Bcache
• Use bcache command instead of echo 1 > /sys/...
• Support of Compound Actions for Bcache without caching device
• Support of Compound Actions for Flash-only Bcache

Pending in Expert Partitioner

• Show Flash-only Bcache devices
• Create Bcache without caching device
• Create/Delete Flash-only Bcache
• Modify Bcache devices (e.g., change the caching device or caching mode)

Done during this sprint

libstorage-ng

• Probe Flash-only Bcache
• Create/Delete Flash-only Bcache (still pending)
• Use bcache command instead of echo 1 > /sys/...
• Support of Compound Actions for Bcache without caching device
• Support of Compound Actions for Flash-only Bcache

Expert Partitioner

• Show Flash-only Bcache devices
• Create Bcache without caching device
• Create/Delete Flash-only Bcache (still pending)
• Modify Bcache devices (still pending)

PBIs

• https://trello.com/c/T7taTEix/606-5-use-the-bcache-command-for-probing
  • PR: openSUSE/libstorage-ng#607
  • PR: yast/yast-storage-ng#829
  • PR: openSUSE/installation-images#293
• https://trello.com/c/sdR0Hwi3/607-2-use-the-new-bcache-command-instead-of-make-bcache
  • PR: openSUSE/libstorage-ng#611
  • PR: yast/yast-storage-ng#834
• https://trello.com/c/GMjxjMJC/654-3-allow-to-create-a-bcache-without-cset
  • PR: yast/yast-storage-ng#838

Screenshots