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VDS_HINTS structure

[Beginning with Windows 8 and Windows Server 2012, the Virtual Disk Service COM interface is superseded by the Windows Storage Management API.]

Defines the automagic hints for a LUN or LUN plex.

Syntax


typedef struct _VDS_HINTS {
  ULONGLONG ullHintMask;
  ULONGLONG ullExpectedMaximumSize;
  ULONG     ulOptimalReadSize;
  ULONG     ulOptimalReadAlignment;
  ULONG     ulOptimalWriteSize;
  ULONG     ulOptimalWriteAlignment;
  ULONG     ulMaximumDriveCount;
  ULONG     ulStripeSize;
  BOOL      bFastCrashRecoveryRequired;
  BOOL      bMostlyReads;
  BOOL      bOptimizeForSequentialReads;
  BOOL      bOptimizeForSequentialWrites;
  BOOL      bRemapEnabled;
  BOOL      bReadBackVerifyEnabled;
  BOOL      bWriteThroughCachingEnabled;
  BOOL      bHardwareChecksumEnabled;
  BOOL      bIsYankable;
  SHORT     sRebuildPriority;
} VDS_HINTS, *PVDS_HINTS;

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.

ValueMeaning
VDS_HINT_FASTCRASHRECOVERYREQUIRED
0x0000000000000001L

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.

VDS_HINT_MOSTLYREADS
0x0000000000000002L

The provider optimizes the LUN for a read-mostly usage pattern, typically by using mirroring rather than parity striping.

VDS_HINT_OPTIMIZEFORSEQUENTIALREADS
0x0000000000000004L

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.

VDS_HINT_OPTIMIZEFORSEQUENTIALWRITES
0x0000000000000008L

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.

VDS_HINT_READBACKVERIFYENABLED
0x0000000000000010L

The provider verifies the writes to the LUN by using readback.

VDS_HINT_REMAPENABLED
0x0000000000000020L

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.

VDS_HINT_WRITETHROUGHCACHINGENABLED
0x0000000000000040L

The provider enables the write-through caching policy on the LUN.

VDS_HINT_HARDWARECHECKSUMENABLED
0x0000000000000080L

The provider enables a hardware checksum on the LUN.

VDS_HINT_ISYANKABLE
0x0000000000000100L

The provider configures 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.

 

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 ullSizeInBytes when the IVdsSubSystem::CreateLun 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.

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 to 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 set to TRUE, the provider verifies the writes to the LUN by readback. If it is set to 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.

sRebuildPriority

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

Remarks

The IVdsSubSystem::CreateLun method passes this structure as a parameter to provide hints for creating a LUN. It is passed as a parameter in the ApplyHints method on both the IVdsLun and IVdsLunPlex interfaces to apply a new set of hints to a LUN or LUN plex, respectively. Further, it is returned by the QueryHints method on both the IVdsLun and IVdsLunPlex interfaces 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

Minimum supported client

Windows Vista [desktop apps only]

Minimum supported server

Windows Server 2003 [desktop apps only]

Header

Vds.h;
VdsHwPrv.h (for hardware providers)

See also

VDS Structures
IVdsLun::ApplyHints
IVdsLun::QueryHints
IVdsLunPlex::ApplyHints
IVdsLunPlex::QueryHints
IVdsSubSystem::CreateLun

 

 

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