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EVA Concepts and terminology

EVA Concepts and terminology

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EVA Concepts and terminology

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  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 HP Restricted

  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 HP Restricted

  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) HP Restricted

  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 HP Restricted

  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 HP Restricted

  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 HP Restricted

  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 HP Restricted

  9. Assigned Disk group capacity Unassigned 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 HP Restricted

  10. Moderately redundant volume (VRAID5) No redundancy volume (VRAID0) Highly redundant volume (VRAID1) VRAID1 pair VRAID1 pair VRAID1 pair VRAID1 pair 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. HP Restricted

  11. LDAD Create volume Insert Pstore Volume 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 HP Restricted

  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 (4+1) 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 HP Restricted

  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 HP Restricted

  14. Create unit LDAD LDAD LDisk SCVD metadata Size redundancy DUnit Writeprotect Cache policy LUN PUnit Virtual disk creation (2 of 2) • Ldisks: Logical disks (containers) • SCVDs: Storage cell virtual disk • Dunits: Derived units • Punits: Presented units HP Restricted

  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 HP Restricted

  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 HP Restricted

  17. Add more disks Moderately redundant volume (VRAID5) + No redundancy volume (VRAID0) Highly redundant volume (VRAID1) VRAID1 pair VRAID1 pair VRAID1 pair VRAID1 pair Additional storage space available Available storage space (equivalent of 3 disks) Moderately redundant volume (VRAID5) No redundancy volume (VRAID0) Highly redundant volume (VRAID1) VRAID1 pair VRAID1 pair VRAID1 pair VRAID1 pair VRAID1 pair VRAID1 pair Virtual disk leveling (2 of 3) • Virtual disk blocks are automatically relocated to level spindle use HP Restricted

  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, 5*36GB, 5*72GB • 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 1:2 • Proportional amounts of disk capacity are used whatever virtual disk capacity is created HP Restricted

  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 HP Restricted

  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 HP Restricted