Detailed Information about CHECKDB Error "Extent (##:##) In Database Id ## Is Marked Allocated In The Gam, But No Sgam Or Iam Has Allocated It"

Symptom:

When using DBCC CHECKDB with REPAIR_ALLOW_DATA_LOSS parameter to repair a corrupt .MDF database, like this:

DBCC CHECKDB(xxxx, ‘REPAIR_ALLOW_DATA_LOSS’)

you see the following error message:

DBCC results for ‘Error1’.
Repair: The extent (1:296) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 0 (type Unknown).
Repair: The extent (1:304) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 0 (type Unknown).
Repair: The extent (1:312) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 0 (type Unknown).
Repair: The extent (1:328) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 0 (type Unknown).
Repair: The extent (1:360) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 0 (type Unknown).
Repair: The extent (1:376) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 0 (type Unknown).
Repair: The extent (1:384) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 0 (type Unknown).
Repair: The extent (1:400) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 0 (type Unknown).
Repair: The page (1:285) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown).
Repair: The page (1:287) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown).
Repair: The page (1:289) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown).
Repair: The page (1:291) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown).
Repair: The page (1:293) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown).
Repair: The page (1:368) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown).
Repair: The page (1:283) has been deallocated from object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597770317824 (type Unknown).
Msg 8948, Level 16, State 3, Line 8
Database error: Page (1:284) is marked with the wrong type in PFS page (1:1). PFS status 0x70 expected 0x60.
The error has been repaired.
Msg 8948, Level 16, State 3, Line 8
Database error: Page (1:286) is marked with the wrong type in PFS page (1:1). PFS status 0x70 expected 0x60.
The error has been repaired.
Msg 8948, Level 16, State 3, Line 8
Database error: Page (1:288) is marked with the wrong type in PFS page (1:1). PFS status 0x70 expected 0x60.
The error has been repaired.
Msg 8948, Level 16, State 3, Line 8
Database error: Page (1:290) is marked with the wrong type in PFS page (1:1). PFS status 0x70 expected 0x60.
The error has been repaired.
Msg 8948, Level 16, State 3, Line 8
Database error: Page (1:292) is marked with the wrong type in PFS page (1:1). PFS status 0x70 expected 0x60.
The error has been repaired.
Msg 8948, Level 16, State 3, Line 8
Database error: Page (1:294) is marked with the wrong type in PFS page (1:1). PFS status 0x70 expected 0x60.
The error has been repaired.
Msg 8948, Level 16, State 3, Line 8
Database error: Page (1:295) is marked with the wrong type in PFS page (1:1). PFS status 0x70 expected 0x60.
The error has been repaired.
Msg 8905, Level 16, State 1, Line 8
Extent (1:296) in database ID 39 is marked allocated in the GAM, but no SGAM or IAM has allocated it.
The error has been repaired.
Msg 8905, Level 16, State 1, Line 8
Extent (1:304) in database ID 39 is marked allocated in the GAM, but no SGAM or IAM has allocated it.
The error has been repaired.
Msg 8905, Level 16, State 1, Line 8
Extent (1:312) in database ID 39 is marked allocated in the GAM, but no SGAM or IAM has allocated it.
The error has been repaired.
Msg 8905, Level 16, State 1, Line 8
Extent (1:328) in database ID 39 is marked allocated in the GAM, but no SGAM or IAM has allocated it.
The error has been repaired.
Msg 8905, Level 16, State 1, Line 8
Extent (1:360) in database ID 39 is marked allocated in the GAM, but no SGAM or IAM has allocated it.
The error has been repaired.
Msg 8928, Level 16, State 6, Line 8
Object ID 0, index ID -1, partition ID 0, alloc unit ID 0 (type Unknown): Page (1:368) could not be processed. See other errors for details.
The error has been repaired.
Msg 8905, Level 16, State 1, Line 8
Extent (1:376) in database ID 39 is marked allocated in the GAM, but no SGAM or IAM has allocated it.
The error has been repaired.
Msg 8905, Level 16, State 1, Line 8
Extent (1:384) in database ID 39 is marked allocated in the GAM, but no SGAM or IAM has allocated it.
The error has been repaired.
Msg 8905, Level 16, State 1, Line 8
Extent (1:400) in database ID 39 is marked allocated in the GAM, but no SGAM or IAM has allocated it.
The error has been repaired.
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 281475001417728 (type Unknown), page ID (1:376) contains an incorrect page ID in its page header. The PageId in the page header = (70:34).
Msg 8906, Level 16, State 1, Line 8
Page (1:284) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘IAM_PG MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 8906, Level 16, State 1, Line 8
Page (1:285) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown), page ID (1:285) contains an incorrect page ID in its page header. The PageId in the page header = (8074:44).
Msg 8906, Level 16, State 1, Line 8
Page (1:286) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘IAM_PG MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 8906, Level 16, State 1, Line 8
Page (1:287) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown), page ID (1:287) contains an incorrect page ID in its page header. The PageId in the page header = (7620:27).
Msg 8906, Level 16, State 1, Line 8
Page (1:288) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘IAM_PG MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 8906, Level 16, State 1, Line 8
Page (1:289) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown), page ID (1:289) contains an incorrect page ID in its page header. The PageId in the page header = (8053:29).
Msg 8906, Level 16, State 1, Line 8
Page (1:290) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘IAM_PG MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 8906, Level 16, State 1, Line 8
Page (1:291) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown), page ID (1:291) contains an incorrect page ID in its page header. The PageId in the page header = (7098:50).
Msg 8906, Level 16, State 1, Line 8
Page (1:292) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘IAM_PG MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 8906, Level 16, State 1, Line 8
Page (1:293) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown), page ID (1:293) contains an incorrect page ID in its page header. The PageId in the page header = (7098:50).
Msg 8906, Level 16, State 1, Line 8
Page (1:294) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘IAM_PG MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 8906, Level 16, State 1, Line 8
Page (1:295) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘IAM_PG MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown), page ID (1:313) contains an incorrect page ID in its page header. The PageId in the page header = (7220:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown), page ID (1:328) contains an incorrect page ID in its page header. The PageId in the page header = (6846:34).
Msg 8906, Level 16, State 1, Line 8
Page (1:368) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘IAM_PG MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown), page ID (1:368) contains an incorrect page ID in its page header. The PageId in the page header = (6:34).
The error has been repaired.
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown), page ID (1:385) contains an incorrect page ID in its page header. The PageId in the page header = (7074:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597764222976 (type Unknown), page ID (1:400) contains an incorrect page ID in its page header. The PageId in the page header = (6818:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597769400320 (type Unknown), page ID (1:296) contains an incorrect page ID in its page header. The PageId in the page header = (4044:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597769465856 (type Unknown), page ID (1:384) contains an incorrect page ID in its page header. The PageId in the page header = (4076:34).
Msg 8906, Level 16, State 1, Line 8
Page (1:283) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597770317824 (type Unknown), page ID (1:283) contains an incorrect page ID in its page header. The PageId in the page header = (3374:54).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597783752704 (type Unknown), page ID (1:297) contains an incorrect page ID in its page header. The PageId in the page header = (10:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597783818240 (type Unknown), page ID (1:298) contains an incorrect page ID in its page header. The PageId in the page header = (18:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597783883776 (type Unknown), page ID (1:299) contains an incorrect page ID in its page header. The PageId in the page header = (42:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597783949312 (type Unknown), page ID (1:300) contains an incorrect page ID in its page header. The PageId in the page header = (14:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597784014848 (type Unknown), page ID (1:301) contains an incorrect page ID in its page header. The PageId in the page header = (14:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597784080384 (type Unknown), page ID (1:302) contains an incorrect page ID in its page header. The PageId in the page header = (32:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597784145920 (type Unknown), page ID (1:303) contains an incorrect page ID in its page header. The PageId in the page header = (56:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597784211456 (type Unknown), page ID (1:304) contains an incorrect page ID in its page header. The PageId in the page header = (34:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597784276992 (type Unknown), page ID (1:305) contains an incorrect page ID in its page header. The PageId in the page header = (30:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597784342528 (type Unknown), page ID (1:306) contains an incorrect page ID in its page header. The PageId in the page header = (10:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597784408064 (type Unknown), page ID (1:307) contains an incorrect page ID in its page header. The PageId in the page header = (98:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597784473600 (type Unknown), page ID (1:308) contains an incorrect page ID in its page header. The PageId in the page header = (34:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597784539136 (type Unknown), page ID (1:309) contains an incorrect page ID in its page header. The PageId in the page header = (20:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597784604672 (type Unknown), page ID (1:310) contains an incorrect page ID in its page header. The PageId in the page header = (38:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597784670208 (type Unknown), page ID (1:311) contains an incorrect page ID in its page header. The PageId in the page header = (30:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597784735744 (type Unknown), page ID (1:312) contains an incorrect page ID in its page header. The PageId in the page header = (32:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597787881472 (type Unknown), page ID (1:360) contains an incorrect page ID in its page header. The PageId in the page header = (24:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597787947008 (type Unknown), page ID (1:361) contains an incorrect page ID in its page header. The PageId in the page header = (6:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597788012544 (type Unknown), page ID (1:362) contains an incorrect page ID in its page header. The PageId in the page header = (30:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597788078080 (type Unknown), page ID (1:363) contains an incorrect page ID in its page header. The PageId in the page header = (60:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597788143616 (type Unknown), page ID (1:364) contains an incorrect page ID in its page header. The PageId in the page header = (36:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597788209152 (type Unknown), page ID (1:365) contains an incorrect page ID in its page header. The PageId in the page header = (8:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597788274688 (type Unknown), page ID (1:366) contains an incorrect page ID in its page header. The PageId in the page header = (50:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597788864512 (type Unknown), page ID (1:367) contains an incorrect page ID in its page header. The PageId in the page header = (24:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597788995584 (type Unknown), page ID (1:377) contains an incorrect page ID in its page header. The PageId in the page header = (34:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597789061120 (type Unknown), page ID (1:378) contains an incorrect page ID in its page header. The PageId in the page header = (52:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597789126656 (type Unknown), page ID (1:379) contains an incorrect page ID in its page header. The PageId in the page header = (90:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597789192192 (type Unknown), page ID (1:380) contains an incorrect page ID in its page header. The PageId in the page header = (34:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597789257728 (type Unknown), page ID (1:381) contains an incorrect page ID in its page header. The PageId in the page header = (52:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597789323264 (type Unknown), page ID (1:382) contains an incorrect page ID in its page header. The PageId in the page header = (76:34).
Msg 8909, Level 16, State 1, Line 8
Table error: Object ID 0, index ID -1, partition ID 0, alloc unit ID 27021597789388800 (type Unknown), page ID (1:383) contains an incorrect page ID in its page header. The PageId in the page header = (16:34).
CHECKDB found 31 allocation errors and 44 consistency errors not associated with any single object.
CHECKDB fixed 31 allocation errors and 0 consistency errors not associated with any single object.
Repair: IAM chain for object ID 27, index ID 2, partition ID 562949955190784, alloc unit ID 562949955190784 (type In-row data), has been truncated before page (1:288) and will be rebuilt.
Msg 2575, Level 16, State 1, Line 8
The Index Allocation Map (IAM) page (1:288) is pointed to by the next pointer of IAM page (0:0) in object ID 27, index ID 2, partition ID 562949955190784, alloc unit ID 562949955190784 (type In-row data), but it was not detected in the scan.
The error has been repaired.
CHECKDB found 1 allocation errors and 0 consistency errors in table ‘sys.sysowners’ (object ID 27).
CHECKDB fixed 1 allocation errors and 0 consistency errors in table ‘sys.sysowners’ (object ID 27).
Repair: The page (1:79) has been allocated to object ID 34, index ID 2, partition ID 562949955649536, alloc unit ID 562949955649536 (type In-row data).
Repair: IAM chain for object ID 34, index ID 2, partition ID 562949955649536, alloc unit ID 562949955649536 (type In-row data), has been truncated before page (1:295) and will be rebuilt.
Repair: The page (1:80) has been allocated to object ID 34, index ID 3, partition ID 844424932360192, alloc unit ID 844424932360192 (type In-row data).
Repair: IAM chain for object ID 34, index ID 3, partition ID 844424932360192, alloc unit ID 844424932360192 (type In-row data), has been truncated before page (1:368) and will be rebuilt.
Msg 8906, Level 16, State 1, Line 8
Page (1:79) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 2575, Level 16, State 1, Line 8
The Index Allocation Map (IAM) page (1:295) is pointed to by the next pointer of IAM page (0:0) in object ID 34, index ID 2, partition ID 562949955649536, alloc unit ID 562949955649536 (type In-row data), but it was not detected in the scan.
The error has been repaired.
Msg 8906, Level 16, State 1, Line 8
Page (1:80) in database ID 39 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags ‘MIXED_EXT ALLOCATED 0_PCT_FULL’.
The error has been repaired.
Msg 2575, Level 16, State 1, Line 8
The Index Allocation Map (IAM) page (1:368) is pointed to by the next pointer of IAM page (0:0) in object ID 34, index ID 3, partition ID 844424932360192, alloc unit ID 844424932360192 (type In-row data), but it was not detected in the scan.
The error has been repaired.
Msg 824, Level 24, State 2, Line 8
SQL Server detected a logical consistency-based I/O error: incorrect pageid (expected 1:261; actual 114:34). It occurred during a read of page (1:261) in database ID 39 at offset 0x0000000020a000 in file ‘C:Program FilesMicrosoft SQL ServerMSSQL12.SQL2014MSSQLDATAError1.mdf’. Additional messages in the SQL Server error log or system event log may provide more detail. This is a severe error condition that threatens database integrity and must be corrected immediately. Complete a full database consistency check (DBCC CHECKDB). This error can be caused by many factors; for more information, see SQL Server Books Online.
Msg 824, Level 24, State 2, Line 8
SQL Server detected a logical consistency-based I/O error: incorrect pageid (expected 1:369; actual 40:60). It occurred during a read of page (1:369) in database ID 39 at offset 0x000000002e2000 in file ‘C:Program FilesMicrosoft SQL ServerMSSQL12.SQL2014MSSQLDATAError1.mdf’. Additional messages in the SQL Server error log or system event log may provide more detail. This is a severe error condition that threatens database integrity and must be corrected immediately. Complete a full database consistency check (DBCC CHECKDB). This error can be caused by many factors; for more information, see SQL Server Books Online.

where ‘Error1’ is name of the corrupt MDF database being repaired.

Msg 8905 indicates an extent is allocated to GAM, but no SGAM or IAM has allocated it. This is an allocation error.

Screenshot of error message:

Precise Explanation:

In MDF database, the data are stored as pages. GAM, SGAM and IAM are all used for allocations. And the data are allocated in the unit of extent(8 pages) instead of one page to improve the performance. If an extent is allocated by GAM but not allocated by SGAM or IAM, then CHECKDB will report Msg 8905, and then try to fix it.

You can use our product DataNumen SQL Recovery to recover the data from the corrupt MDF file and solve this error.

Sample File 1:

Sample corrupt MDF files on which CHECKDB REPAIR_ALLOW_DATA_LOSS will find Msg 8905 error, but NOT be able to recover the database, while DataNumen SQL Recovery can.

SQL Server version	Corrupt MDF file	MDF file fixed by DataNumen SQL Recovery
SQL Server 2014	Error11.mdf	Error11_fixed.mdf