xlog flush request is not satisfied in log files Today I saw that Postgres produces error messages related to possible data corruption (?). Everything's working as expected so I didn't realize anything was wrong. 

ERROR:  xlog flush request 6E/82FFED10 is not satisfied --- flushed only to 3D/CA02E920
CONTEXT:  writing block 1008 of relation base/118517/118823
CONTEXT:  writing block 1008 of relation base/118517/118823
WARNING:  could not write block 1008 of base/118517/118823
LOG:  request to flush past end of generated WAL; request 6E/82FFED10, currpos 3D/CA02E920
DETAIL:  Multiple failures --- write error might be permanent.


PostgreSQL 11. 
Configuration:

max_connections = 100
shared_buffers = 16GB
effective_cache_size = 48GB
maintenance_work_mem = 2GB
checkpoint_completion_target = 0.7
wal_buffers = 16MB
default_statistics_target = 100
random_page_cost = 1.1
effective_io_concurrency = 200
work_mem = 41943kB
min_wal_size = 1GB
max_wal_size = 2GB
max_worker_processes = 8
max_parallel_workers_per_gather = 4
max_parallel_workers = 8


pg_control version number:            1100
Catalog version number:               201809051
Database system identifier:           6775130872383000604
Database cluster state:               in production
pg_control last modified:             Thu Mar 12 04:46:20 2020
Latest checkpoint location:           85/802C9268
Latest checkpoint's REDO location:    85/802C9230
Latest checkpoint's REDO WAL file:    000000010000008500000080
Latest checkpoint's TimeLineID:       1
Latest checkpoint's PrevTimeLineID:   1
Latest checkpoint's full_page_writes: on
Latest checkpoint's NextXID:          0:69393025
Latest checkpoint's NextOID:          511846
Latest checkpoint's NextMultiXactId:  11365
Latest checkpoint's NextMultiOffset:  23069
Latest checkpoint's oldestXID:        562
Latest checkpoint's oldestXID's DB:   1
Latest checkpoint's oldestActiveXID:  69393025
Latest checkpoint's oldestMultiXid:   1
Latest checkpoint's oldestMulti's DB: 1
Latest checkpoint's oldestCommitTsXid:0
Latest checkpoint's newestCommitTsXid:0
Time of latest checkpoint:            Thu Mar 12 04:45:50 2020
Fake LSN counter for unlogged rels:   0/1
Minimum recovery ending location:     0/0
Min recovery ending loc's timeline:   0
Backup start location:                0/0
Backup end location:                  0/0
End-of-backup record required:        no
wal_level setting:                    replica
wal_log_hints setting:                off
max_connections setting:              100
max_worker_processes setting:         8
max_prepared_xacts setting:           0
max_locks_per_xact setting:           64
track_commit_timestamp setting:       off
Maximum data alignment:               8
Database block size:                  8192
Blocks per segment of large relation: 131072
WAL block size:                       8192
Bytes per WAL segment:                16777216
Maximum length of identifiers:        64
Maximum columns in an index:          32
Maximum size of a TOAST chunk:        1996
Size of a large-object chunk:         2048
Date/time type storage:               64-bit integers
Float4 argument passing:              by value
Float8 argument passing:              by value
Data page checksum version:           0
Mock authentication nonce:            edec50c3ef6ee1a42351c2e593de539feb25343ad239e12b813b4c212ae2a1d6


I did a backup and then I restored it to another database and removed the old one. It didn't work. I still getting those errors.

P.S. PostgreSQL did not crash lately. There is also a plenty of space on SSD.
Yes that looks like corruption, perhaps caused by storage hardware problems.

Perform a pg_dumpall of the cluster and restore it to a newly created cluster, that should get rid of the problem.

Check your hardware.