EVA Concepts and terminology

1
EVA Concepts and terminology
Yu-Sheng Guo Account Support Consultant HP Taiwan
2
Objectives

• Define the virtual storage terms applicable to
  the EVA
• Name the primary features of a disk group and
  default disk group
• Describe the ways in which disk groups are
  configured
• Name the primary features of virtual disks
• Differentiate between conventional RAID and
  distributed virtual RAID (VRAID) technology

3
Virtual storage terminology

• Storage system (cell) An initialized pair of
  HSV controllers with a minimum of eight physical
  disk drives
• Disk group A group of physical disks, from
  which you can create virtual disks
• Virtual disk A logical disk with certain
  characteristics, residing in a disk group
• Virtual disk leveling Distribution of all user
  data within the virtual disks in a disk group
  across all physical disks within the disk group
• Distributed sparing Allocated space per disk
  group to recover from physical disk failure in
  that disk group
• Host A collection of host bus adapters that
  reside in the same (virtual) server
• Logical Unit Number (LUN) A virtual disk
  presented to one or multiple hosts

4
Storage system

• Also called a cell, an initialized pair of HSV
  controllers with a minimum of eight physical disk
  drives
• Requires a name up to 20 characters long
• Special characters are not allowed (for example,
  ?, , /, \)
• Two consecutive spaces are not allowed
• Name is changeable
• System initialization
• Makes the storage system ready for use
• Binds the controllers together as an operational
  pair
• Creates the first disk group
• Establishes preliminary data structures on the
  disk array (metadata)

5
Storage system metadata

• System-level metadata is stored on quorum disks
  and contains
• Controller information
• WWN and cell name
• Character map of disk groups and virtual disk
  members

6
Disk group

• A group of physical disks
• Maximum of 16 disk groups per array (7 for an
  eva3000)
• Minimum number of physical disk drives in a disk
  group is 8
• Maximum number of physical disk drives is the
  number present in the system up to 240 (up to 56
  for the eva3000)
• Unassigned or new disks can be added to an
  existing group
• Mixed drive sizes within a group are allowed
• Disk failure protection level
• None, single, or double disk failures (not
  concurrent failure)
• Default is none (sparing will occur from
  unassigned capacity)
• Space is allocated in 2MB segments (PSEGs)
• Chunk size is 256 blocks (128KB), fixed

7
Default disk group

• First disk group created
• Used like any other disk group
• Can be deleted after another disk group is
  created to protect metadata
• Can be renamed

8
Disk group metadata

• When a cell is created, there are five quorum
  disks in the default disk group
• Maximum of 16 quorum disks (one per disk group)
• When a new disk group is created
• One quorum disk is created on it
• One quorum disk is removed from the default disk
  group until just one quorum disk remains
• Metadata overhead is ? 0.2 of total disk group
  capacity

9
Disk group capacity

• Disk group has two types of capacity
• Assigned capacity
• Virtual disks, snapshots and clones
• Spare space reserved for the protection level
• Unassigned capacity
• New virtual disk creation, snapshots and clones
• Freeing a physical disk for removal or
  reassignment
• Data reconstruction after disk failure
• Increases when virtual disks are deleted or new
  physical disks are added to the disk group

10
Disk group member terms

• Unpaired The disk that does not contain VRAID1
  (mirrored) data on it because the disk group was
  created with an odd number of drives or because
  it lost its mirror partner because of a failure
• Paired The disk that was previously unpaired. A
  disk was added to the group, which now contains
  an even number of disks.

11
Disk group creation

• Physical stores (Pstores)
• Raw FC-AL disks
• Volumes
• Pstores metadata
• Logical disk allocation domain (LDAD)
• Grouping of physical disks
• Commonly called a disk group

12
Virtual disk

• A logical disk with certain attributes, such as
  size and VRAID level, residing in a disk group
  and spanning all members of the disk group
• Minimum size of 1GB and maximum size of 2TB (less
  1GB)
• Maximum of 512 virtual disks
• VRAID levels for the virtual disks
• VRAID0 or striping (none)
• Distributed across all disk in a group
• 100 of disk group capacity
• VRAID5 or striping with parity (moderate)
• Distributed across all disk in a group
• Always five (41) physical disks per stripe are
  used
• 80 of disk group capacity
• VRAID1 or mirroring (high)
• Two physical disks per mirror are used
• The odd drive in a disk group will not
  participate in this virtual disk
• 50 of disk group capacity

13
Virtual disk creation (1 of 2)

• First written bit (first write overhead)
• HSV tracks blocks written on a virtual disk
• Allows easy movement of data for snaps and clones
• Zeros are not used in advance because operations
  involving copies or moves would include the zeros
• First write to a block in a new LUN requires a
  metadata update
• Subsequent writes touch only the block, not
  metadata
• For normal uses with high I/O rates, overhead not
  an issue
• For performance testing, where write performance
  is critical, this overhead can be critical
• Eliminate first-write overhead
• Write all data blocks once before conducting a
  test

14
Virtual disk creation (2 of 2)

• Ldisks Logical disks (containers)
• SCVDs Storage cell virtual disk
• Dunits Derived units
• Punits Presented units

15
Virtual disk map

• Contains pointers that identify which virtual
  disks use which chunks of capacity
• Map is read into HSV controllers during boot
• Map is written on state change of disk group
• Disk drive failure
• Disk drives added or removed
• Traditional snapshot created
• Snapclone fully copied
• Virtual disk added or deleted
• Virtual disk enlarged
• Each write I/O to a virtual disk that has
  demand-allocated snapshot

16
Virtual disk leveling (1 of 3)

• Distribution of all data within virtual disks
  proportionally across all physical disks within
  the disk group
• Leveling takes place when
• Disk devices are added to a disk group
• Disk devices can be added one or more at a time
• Disk devices are ungrouped from a disk group
• You can only do this one disk at a time
• Disk devices within a disk group fail (assuming
  VRAID survival)
• Leveling is dynamic (there is no user control)
• Leveling is detectable through Command View EVA

17
Virtual disk leveling (2 of 3)

• Virtual disk blocks are automatically relocated
  to level spindle use

18
Virtual disk leveling (3 of 3)

• Leveling takes place when disk group members vary
  in size
• Example 1 Disk group 10 drives, all 36GB
• If a virtual disk is created using all of the
  drives, each 36GB disk contains an equal share
  (10) of the capacity
• Example 2 Disk group 10 drives, 536GB, 572GB
• If a virtual disk is created using all of the
  drives
• Each 36GB and 72GB disk contains a proportional
  share of the capacity
• The proportion maintained in this example must be
  12
• Proportional amounts of disk capacity are used
  whatever virtual disk capacity is created

19
Virtual disk expansion

• Once a virtual disk is created, you can increase
  the size, but not decrease it
• Supported on Sun Solaris with the growfs command
• Supported on Windows 2000
• It is not supported on any other operating system
• Workarounds are available
• Described in installation and configuration
  guides for each OS

20
Hosts and LUNs

• A host is a collection of host bus adapters that
  reside in the same (virtual) server
• A LUN is a virtual disk presented to one or
  multiple hosts
• Rules for hosts, connections, and LUNs
• A maximum of 256 hosts
• A maximum of 1,024 Fibre Channel adapter
  connections
• A maximum of 256 LUNs on any one Fibre Channel
  adapter
• A maximum of 8,192 presentations of LUNs to hosts
• Examples
• 1 LUN presented to 1 host 1 presentation
• 1 LUN presented to 256 hosts 256 presentations
• 256 LUNs presented to 1 host each 256
  presentations

21
(No Transcript)