Storage Integration with Host-based Write-back Caching

Transcription

1 Storage Integration with Host-based Write-back Caching Andy NetApp SolidFire Santa Clara, CA 1

2 Agenda Patented information How virtual machines use storage Caching methods And who can and needs to use them Single-host write-back caching integration High Availability write-back caching integration Santa Clara, CA 2

3 Patented information Authors: Andy Banta and Erik Cota-Robles Wholly owned by VMware Discovery is fully described by the patent Not giving away any secrets here Santa Clara, CA 3

4 How VMware uses storage Shared filesystem on block storage Others exist, not as interesting One or more LUs make up one filesystem Virtual disks intermixed with metadata Various locks to prevent or coordinate concurrent access to VMs and metadata. Santa Clara, CA 4

5 VMFS layout VMFS LBA 0 META DATA Virtual disk data META DATA Virtual disk data Virtual disk data META DATA Virtual disk data META DATA Santa Clara, CA 5

6 Caching with VMFS Hosts can t cache metadata Heartbeat operations assure storage health Used to coordinate access among multiple hosts Information about usage and layout Hosts can cache virtual disk data Assuming single host access Assuming no underlying storage operations Santa Clara, CA 6

7 Write-back vs. Write-through Write-through Write operations complete to backing storage Therefore no write speed up Provides transactional consistency Required in many cases Write-back Speeds up write operations Might cause data corruption or loss Santa Clara, CA 7

8 Write-back options Write ordering is important Flushing should be in write order Out-of-order flush can cause corruption Not for all workloads Desktops, web servers are OK Databases not so much Can be used for crash consistency Santa Clara, CA 8

9 Write ordering corruption Santa Clara, CA 9

10 Write-back pitfalls Host Storage doesn t have an up-to-date representation of written data 1 Santa Clara, CA 10

11 Write-back pitfalls Host Incomplete data for storage-based snapshot or replication operations 1 Santa Clara, CA 11

12 Write-back pitfalls Host Inconsistency between hosts for simultaneous access or vmotion Host 2 1 Santa Clara, CA 12

13 Storage Integration with host-based write-back caching Santa Clara, CA 13

14 New commands and responses Simple expansion of SCSI T10 standard Cache Notification Command Capability discoverable at Inquiry Host informs storage of intent to do write-back caching Provides a range of blocks (LBAs) Cache Flushed Command Flag to indicate if caching is complete Santa Clara, CA 14

15 New commands and responses Simple expansion of SCSI T10 standard Flush Required Unit Attention Recoverable, Not ignorable Synchronized with Flush Completed command Flag for one time or permanent Santa Clara, CA 15

16 No caching scenario Santa Clara, CA 16

17 Start caching example Santa Clara, CA 17

18 One time flush Storage based operations such as snapshot or replication Santa Clara, CA 18

19 Disable caching Simultaneous access going on, such as vmotion or clustered VMs Santa Clara, CA 19

20 Terminate caching Host terminates caching for whatever reason Santa Clara, CA 20

21 Cache coordination Action Unit Attention Host Command Storage operation Flush Required one time Flush complete - No Cache complete Secondary host operation Primary host operation Flush Required - permanent N/A Flush complete Cache complete Flush complete Cache complete Santa Clara, CA 21

22 VMware Fault Tolerance Running in lockstep Santa Clara, CA 22

23 Fault Tolerance with write-back caching Santa Clara, CA 23

24 New commands and responses Continued expansion of SCSI T10 standard Cache Notification Command Standby Present indicator Assuming Control indicator Write Query Command Checks if particular LBAs have been written Used to prune the standby write-back cache Santa Clara, CA 24

25 Initiate write-back caching with standby Santa Clara, CA 25

26 Standby checking cache status Santa Clara, CA 26

27 Fault tolerance example Primary Standby 1 1 Santa Clara, CA 27

28 Fault tolerance example Primary Standby Santa Clara, CA 28

29 Fault tolerance example Primary Standby Santa Clara, CA 29

30 Fault tolerance example Primary Standby Write Query Santa Clara, CA 30

31 Fault tolerance example Primary Standby Write Query response 1 2 Santa Clara, CA 31

32 Fault tolerance example Primary Standby Santa Clara, CA 32

33 Fault tolerance example Primary New Primary Write Query Santa Clara, CA 33

34 Fault tolerance example Primary New Primary Write (flush) Santa Clara, CA 34

35 Failover to secondary system Santa Clara, CA 35

36 Questions? Thank You

37 Free-format slide title Santa Clara, CA 37