VDS_HINTS2 structure (vdshwprv.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[Beginning with Windows 8 and Windows Server 2012, the Virtual Disk Service COM interface is superseded by the Windows Storage Management API.]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.
| Value | Meaning |
|---|---|
|
The provider limits the time that is required for recovery. To support fast recovery, the provider uses a change log that enables the provider to recover the LUN without comparing the entire contents of the LUN. |
|
The provider optimizes the LUN for a read-mostly usage pattern, typically by using mirroring rather than parity striping. |
|
The provider optimizes the LUN for a sequential-read usage pattern. If this flag is not set and VDS_HINT_OPTIMIZEFORSEQUENTIALWRITES is also not set, the LUN is optimized for random I/O. |
|
The provider optimizes the LUN for a sequential-write usage pattern. If this flag is not set and VDS_HINT_OPTIMIZEFORSEQUENTIALREADS is also not set, the LUN is optimized for random I/O. |
|
The provider verifies the writes to the LUN by using readback. |
|
The mapping of LUN extents to drive extents is created and updated automatically by the provider. If this flag is not set, the mapping remains fixed after configuration, except when proactive actions are taken to avoid drive failures. |
|
The provider enables the write-through caching policy on the LUN. |
|
The provider enables a hardware checksum on the LUN. |
|
The provider configures the LUN so that the drives that contribute to it can be physically removed with minimal system disruption. This is normally accomplished by ensuring that the LUN occupies as few drives as possible. |
|
The provider allocates a hot spare for the LUN. For more information, see Hot Sparing, VDS_DRIVE_FLAG, and VDS_DISK_FLAG. |
|
The provider uses the specified bus type on the LUN. For more information, see VDS_STORAGE_BUS_TYPE. |
|
The provider uses a mirrored cache on the LUN. See the VDS_SF_SUPPORTS_MIRRORED_CACHE value of the VDS_SUB_SYSTEM_FLAG enumeration. |
|
The provider enables read caching on the LUN. See the VDS_LF_READ_CACHE_ENABLED value of the VDS_LUN_FLAG enumeration and the VDS_SF_READ_CACHING_CAPABLE value of the VDS_SUB_SYSTEM_FLAG enumeration. |
|
The provider enables write caching on the LUN. See the VDS_LF_WRITE_CACHE_ENABLED value of the VDS_LUN_FLAG enumeration and the VDS_SF_WRITE_CACHING_CAPABLE value of the VDS_SUB_SYSTEM_FLAG enumeration. |
|
The provider enables media scanning on the LUN. See the VDS_LF_MEDIA_SCAN_ENABLED value of the VDS_LUN_FLAG enumeration and the VDS_SF_MEDIA_SCAN_CAPABLE value of the VDS_SUB_SYSTEM_FLAG enumeration. |
|
The provider enables consistency checking on the LUN. See the VDS_LF_CONSISTENCY_CHECK_ENABLED value of the VDS_LUN_FLAG enumeration and the VDS_SF_CONSISTENCY_CHECK_CAPABLE value of the VDS_SUB_SYSTEM_FLAG enumeration. |
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
| Requirement | Value |
|---|---|
| Minimum supported client | Windows 7 [desktop apps only] |
| Minimum supported server | Windows Server 2008 R2 [desktop apps only] |
| Header | vdshwprv.h |