Friday, September 27, 2013

OOW Notes - ASM New Features on 12c

Thursday 12:30 - ASM New features

  • simple idea
  • 1to1 ASM to server
  • shared disk groups
  • wide file striping
  • 10years old in oracle database

grid computing .. cloud computing
  • more consolidation → more database instances per node
  • more clustering → more nodes in clusters
  • larger storage configurations

ASM evolves
  • maximize ASM robustness because increased number of database instances running on large servers
  • minimize ASM overhead because of large clusters
  • minimize cluster reconfiguration overhead because of large clusters

engineered systems (EXADATA and database appliance)
  • complete solutions
  • optimized for a particular objective
  • storage management provided by ASM
  • storage cells provides management offloading

flex ASM (NEW)
  • eliminate requirement for an ASM instance on every cluster server
  • database instances connect any ASM instance in the clustering database instances can failover to a secondary ASM instance
  • admins specify the cardinality of the ASM instances (default 3)

ASM network
in the previous version an oracle cluster required:
  • public network for client applications
  • one or more private networks for interconnect communication within the cluster

remote access (NEW)
in the previous versions database instances use os authentication to connect ASM
ASM clients and the server are always on the same server so this should change

12c database instance and ASM servers can be on different servers
  • flex ASM users password file authentication
  • password file in the ASM diskgroup
  • default config. is configured with the ASM installation

other flex features
  • increased mac number of disks to 511 (previous 63)
  • command for renaming ASM disk
  • ASM instance patch-level verification
  • replicated physical metadata
  • improves reliability
  • virtual metadata has always been replicated with ASM mirroring

admins can now specify a failure group repair time (NEW)
  • similar to existing disk repair time
  • new diskgroup attributes; failgroup_repair_time
  • default time 24 hours
  • power limit can be set for disk resync. operations
  • Conceptually similar to power limit setting for disk group rebalance
  • rebalance: 1 (least resource) to 1024 most resources

disk rescync now check points (NEW)
interrupted resync operations are automatic restart

sometimes rebalance operations are required to restore redundancy.
a disk fails and no replacement available
HBA containing a failure group goes offline

  • with oracle database flex ASM optimized reorganization
  • critical files such as control files log files are restored before datafiles
  • secondary failure is less likely result in critical file loss

  • admins can now specify the content type for each disk group:
  • new disk group attribute; content.type (possible values data, recovery or system)

  • disk group primary/secondary partnering changes with content.type
  • decreases likelihood that multiple failures cause data loss

silent data corruption is a fact in todays storage world
  • database checks for logical consistency when reading data
  • if a logical corruption is detected then automatic recovery can be performed using ASM mirror copies
  • for seldom accessed data, over time all mirror copies of the data could be corrupted

  • with oracle db 12c data can be proactively scrubbed (NEW)
  • scrubbing occurs automatically during rebalance operations
  • with flex ASM, most rebalance tasks offloaded to EXADATA storage
  • each offload request can replace numerous IO

IO distribution in 12c (NEW)
  • each read request is sent to at least loaded available disk
  • even read is transparent to apps and enabled default
  • users on IO bound systems should notice a performance improvement

managing flex ASM (nothing changes)

  • srvctl status asm
  • srvctl modifiy asm -count 4
  • srvctl start asm -n node_name
  • srvctl stop asm -n nodename

ASM Trivia's

why power limit setting value to 11. Why 11?

what was it is called before ASM?

all asm file extent pointers are protected from corruption by XORing to a constant.. what is that constant? 42

The acronym describing ASM data allocation and protection policy is LIKE what?

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