dbcc checkdb gives error "Incorrect PFS free space information for page"
Thank You for response John! 

Tried to backup DB and rebuild clustered index, but didn't help. As I understand there is no patch, but it is and old bug. Or something was really damaged during hardware crash..

This helped:

--dbcc checkdb;
--dbcc checktable(DocStreams) WITH ALL_ERRORMSGS;

ALTER DATABASE WSS_Content
SET SINGLE_USER WITH ROLLBACK IMMEDIATE

dbcc checktable(DocStreams, REPAIR_FAST) WITH ALL_ERRORMSGS;
GO
dbcc checktable(DocStreams, REPAIR_REBUILD) WITH ALL_ERRORMSGS;

-- use this only if above does not work
--DBCC CHECKTABLE(DocStreams, REPAIR_ALLOW_DATA_LOSS) WITH ALL_ERRORMSGS;

ALTER DATABASE WSS_Content SET MULTI_USER;


But first 


Do backup database
I also backuped table using this cmd (press Enter multiple times):

bcp WSS_Content.dbo.DocStreams out C:\backups\DocStreams\DocStreams.dat -t -T

pause


Use in Your own risk)

links:
  incorrect-pfs
  bcp tool

Upd.: or You can try "reorganize with (lob_compaction = on)" first (link)