VDS_HINTS2 structure (vds.h)

[Beginning with Windows 8 and Windows Server 2012, the Virtual Disk Service COM interface is superseded by the Windows Storage Management API.]

Contains the automagic hints for a LUN in a storage pool.

Syntax

typedef struct _VDS_HINTS2 {
  ULONGLONG            ullHintMask;
  ULONGLONG            ullExpectedMaximumSize;
  ULONG                ulOptimalReadSize;
  ULONG                ulOptimalReadAlignment;
  ULONG                ulOptimalWriteSize;
  ULONG                ulOptimalWriteAlignment;
  ULONG                ulMaximumDriveCount;
  ULONG                ulStripeSize;
  ULONG                ulReserved1;
  ULONG                ulReserved2;
  ULONG                ulReserved3;
  BOOL                 bFastCrashRecoveryRequired;
  BOOL                 bMostlyReads;
  BOOL                 bOptimizeForSequentialReads;
  BOOL                 bOptimizeForSequentialWrites;
  BOOL                 bRemapEnabled;
  BOOL                 bReadBackVerifyEnabled;
  BOOL                 bWriteThroughCachingEnabled;
  BOOL                 bHardwareChecksumEnabled;
  BOOL                 bIsYankable;
  BOOL                 bAllocateHotSpare;
  BOOL                 bUseMirroredCache;
  BOOL                 bReadCachingEnabled;
  BOOL                 bWriteCachingEnabled;
  BOOL                 bMediaScanEnabled;
  BOOL                 bConsistencyCheckEnabled;
  VDS_STORAGE_BUS_TYPE BusType;
  BOOL                 bReserved1;
  BOOL                 bReserved2;
  BOOL                 bReserved3;
  SHORT                sRebuildPriority;
} VDS_HINTS2, *PVDS_HINTS2;

Members

ullHintMask

The LUN hint mask. Each of the BOOL members of this structure has a corresponding hint flag that can be set in the mask. If the hint flag is set, the corresponding hint is considered. If the hint flag is not set, the hint is ignored. The hint flags are described in the following table.

ullExpectedMaximumSize

The maximum size to which the LUN is expected to grow, in bytes. The value can be equal to, greater than, or less than the value specified in the ullSizeInBytes parameter when the IVdsHwProviderStoragePools::CreateLunInStoragePool method is called. Some providers use this value to reserve space for the LUN. Providers that are unable to reserve space typically ignore this parameter.

ulOptimalReadSize

The optimal read size for the LUN, in bytes. Zero indicates no optimal read size.

ulOptimalReadAlignment

The optimal read alignment with respect to the first logical block of the LUN. Zero indicates no optimal read alignment.

ulOptimalWriteSize

The optimal write size for the LUN, in bytes. Zero indicates no optimal write size.

ulOptimalWriteAlignment

The optimal write alignment with respect to the first logical block of the LUN. Zero indicates no optimal write alignment.

ulMaximumDriveCount

The maximum number of drives to contribute to the LUN. Zero indicates no maximum drive count. This value can be used to limit the number of stripe interleaves in a stripe set.

ulStripeSize

The mirror or parity stripe interleave size, in bytes. Zero leaves the stripe size unspecified.

ulReserved1

This member is reserved for future use. Do not use.

ulReserved2

This member is reserved for future use. Do not use.

ulReserved3

This member is reserved for future use. Do not use.

bFastCrashRecoveryRequired

If this member is TRUE, the recovery time is limited. Set the VDS_HINT_FASTCRASHRECOVERYREQUIRED flag in the ullHintMask member to indicate interest in this member.

bMostlyReads

To optimize for a mostly-reads usage pattern (for example, through mirroring rather than parity striping), set this member to TRUE. Otherwise, set it to FALSE. Set the VDS_HINT_MOSTLYREADS flag in the ullHintMask member to indicate interest in this member.

bOptimizeForSequentialReads

To optimize for a sequential-reads usage pattern, set this member to TRUE. Otherwise, set it to FALSE. Setting the bOptimizeForSequentialReads and bOptimizeForSequentialWrites members both to FALSE optimizes for random I/O. Set the VDS_HINT_OPTIMIZEFORSEQUENTIALREADS flag in the ullHintMask member to indicate interest in this member.

bOptimizeForSequentialWrites

To optimize for a sequential-writes usage pattern, set this member to TRUE. Otherwise, set it to FALSE. Setting the bOptimizeForSequentialReads and bOptimizeForSequentialWrites members both to FALSE optimizes for random I/O. Set the VDS_HINT_OPTIMIZEFORSEQUENTIALWRITES flag in the ullHintMask member to indicate interest in this member.

bRemapEnabled

If this member is TRUE, the provider remaps LUN extents to drive extents automatically. If it is FALSE, the mapping of LUN extents to drive extents remains fixed after LUN configuration unless extents are explicitly remapped to avoid corrupted blocks. Set the VDS_HINT_REMAPENABLED flag in the ullHintMask member to indicate interest in this member.

bReadBackVerifyEnabled

If this member is TRUE, the provider verifies the writes to the LUN by readback. If it is FALSE, the provider does not verify writes. Set the VDS_HINT_READBACKVERIFYENABLED flag in the ullHintMask member to indicate interest in this member.

bWriteThroughCachingEnabled

If this member is TRUE, the provider enables write-through caching on the LUN; if it is FALSE, the provider does not enable write-through caching. Set the VDS_HINT_WRITETHROUGHCACHINGENABLED flag in the ullHintMask member to indicate interest in this member.

bHardwareChecksumEnabled

If this member is TRUE, the provider enables a checksum on the LUN. Set the VDS_HINT_HARDWARECHECKSUMENABLED flag in the ullHintMask member to indicate interest in this member.

bIsYankable

If this member is TRUE, the drives that contribute to the LUN can be physically removed without significant disruption to the system (this is typically true when the LUN is composed of extents from only a few drives). If it is FALSE, the LUN cannot be removed without significant disruption to the system. Set the VDS_HINT_ISYANKABLE flag in the ullHintMask member to indicate interest in this member.

bAllocateHotSpare

TRUE if the client wants to allocate a hot spare drive for this LUN, or FALSE otherwise. Set the VDS_HINT_ALLOCATEHOTSPARE flag in the ullHintMask member to indicate interest in this member.

bUseMirroredCache

TRUE if the client wants this LUN to use a mirrored cache, or FALSE otherwise. Set the VDS_HINT_USEMIRROREDCACHE flag in the ullHintMask member to indicate interest in this member.

bReadCachingEnabled

TRUE if the client wants the LUN to use read caching, or FALSE otherwise. Set the VDS_HINT_READCACHINGENABLED flag in the ullHintMask member to indicate interest in this member.

bWriteCachingEnabled

TRUE if the client wants the LUN to use write caching, or FALSE otherwise. Set the VDS_HINT_WRITECACHINGENABLED flag in the ullHintMask member to indicate interest in this member.

bMediaScanEnabled

TRUE if the client wants to enable media scanning for this LUN, or FALSE otherwise. Set the VDS_HINT_MEDIASCANENABLED flag in the ullHintMask member to indicate interest in this member.

bConsistencyCheckEnabled

TRUE if the client wants to enable consistency checking for this LUN, or FALSE otherwise. Set the VDS_HINT_CONSISTENCYCHECKENABLED flag in the ullHintMask member to indicate interest in this member.

BusType

A VDS_STORAGE_BUS_TYPE enumeration value that specifies the bus type for the LUN. Set the VDS_HINT_BUSTYPE flag in the ullHintMask member to indicate interest in this member.

bReserved1

This member is reserved for future use. Do not use.

bReserved2

This member is reserved for future use. Do not use.

bReserved3

This member is reserved for future use. Do not use.

sRebuildPriority

The rebuild priority for the LUN. The value can range from 0 (lowest priority) through 15 (highest priority).

Remarks

The IVdsHwProviderStoragePools::CreateLunInStoragePool method passes this structure as a parameter to provide hints for creating a LUN in a storage pool. It is passed as a parameter in the IVdsLun2::ApplyHints2 method to apply a new set of hints to a LUN. Further, it is returned by the IVdsLun2::QueryHints2 method to report hints currently applied to a LUN or LUN plex, respectively.

Hints are not directives to implementers. While implementers are in general expected to do their best to take hints into consideration, they are not obligated to follow them. Implementers can opt for alternatives when unable to follow specified hints for technical reasons or when following them can result in a poor configuration.

Requirements

See also

IVdsLun2::ApplyHints2

IVdsLun2::QueryHints2