* (1 / POWER (2.0, 16)) - right shift, reciprocal of left shiftĪn example of when you might use this information/code is during programmatic analysis of a corrupt database that DBCC CHECKDB cannot process to allow you to extract data as a last resort. ![]() The T-SQL for this involves floating point math as we need to use the reciprocal of POWER:ĬONVERT (FLOAT, (1 / POWER (2.0, 48)) - right shift, reciprocal of left shiftĬONVERT (FLOAT, - * CONVERT (BIGINT, POWER (2.0, 48)))) m_objId = ( AllocUnitId – ( m_indexId > 16.AllocUnitId = A | B (where | is a logical OR operation).Take the m_objId and left-shift by 16, giving value B. ![]() Take the m_indexId and left-shift by 48, giving value A.M_xactReserved = 0 m_xdesId = (0:0) m_ghostRecCnt = 0 If you have lots of large files, keeping it higher will increase the system performance by having less blocks to seek. If you have lots of small files, then it’s a good idea to keep the allocation size small so your harddrive space won’t be wasted. Pminlen = 8 m_slotCnt = 1 m_freeCnt = 8069 Basically, the allocation unit size is the block size on your hard drive when it formats NTFS. This is because NTFS is limited to 232 -1 clusters. With that allocation unit size, the maximum NTFS volume size is 16 TB. Metadata: PartitionId = 72057594039304192 Metadata: IndexId = 0 Due to the maximum allocation unit size for those two features is 4,096 bytes. M_objId (AllocUnitId.idObj) = 97 m_indexId (AllocUnitId.idInd) = 256 M_typeFlagBits = 0x0 m_level = 0 m_flagBits = 0xa000 Page = (1:445) m_headerVersion = 1 m_type = 1 Basically everything prefixed with ‘Metadata:’ in the DBCC PAGE output below is NOT stored on the page itself: When DBCC PAGE dumps a page header’s contents, it does the necessary calculations and metadata look-ups to be able to tell you the allocation unit ID, partition ID, relational object ID, and relational index ID. What is allocation unit Meaning of allocation. ![]() It’s been a long time since I’ve written a post about pure internals, but every so often I get asked how an allocation unit ID is calculated from the m_objId and m_indexId fields that are stored in the header of every page. Looking for online definition of allocation unit in the Medical Dictionary allocation unit explanation free.
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