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1.. SPDX-License-Identifier: GPL-2.02 3Super Block4-----------5 6The superblock records various information about the enclosing7filesystem, such as block counts, inode counts, supported features,8maintenance information, and more.9 10If the sparse_super feature flag is set, redundant copies of the11superblock and group descriptors are kept only in the groups whose group12number is either 0 or a power of 3, 5, or 7. If the flag is not set,13redundant copies are kept in all groups.14 15The superblock checksum is calculated against the superblock structure,16which includes the FS UUID.17 18The ext4 superblock is laid out as follows in19``struct ext4_super_block``:20 21.. list-table::22 :widths: 8 8 24 4023 :header-rows: 124 25 * - Offset26 - Size27 - Name28 - Description29 * - 0x030 - __le3231 - s_inodes_count32 - Total inode count.33 * - 0x434 - __le3235 - s_blocks_count_lo36 - Total block count.37 * - 0x838 - __le3239 - s_r_blocks_count_lo40 - This number of blocks can only be allocated by the super-user.41 * - 0xC42 - __le3243 - s_free_blocks_count_lo44 - Free block count.45 * - 0x1046 - __le3247 - s_free_inodes_count48 - Free inode count.49 * - 0x1450 - __le3251 - s_first_data_block52 - First data block. This must be at least 1 for 1k-block filesystems and53 is typically 0 for all other block sizes.54 * - 0x1855 - __le3256 - s_log_block_size57 - Block size is 2 ^ (10 + s_log_block_size).58 * - 0x1C59 - __le3260 - s_log_cluster_size61 - Cluster size is 2 ^ (10 + s_log_cluster_size) blocks if bigalloc is62 enabled. Otherwise s_log_cluster_size must equal s_log_block_size.63 * - 0x2064 - __le3265 - s_blocks_per_group66 - Blocks per group.67 * - 0x2468 - __le3269 - s_clusters_per_group70 - Clusters per group, if bigalloc is enabled. Otherwise71 s_clusters_per_group must equal s_blocks_per_group.72 * - 0x2873 - __le3274 - s_inodes_per_group75 - Inodes per group.76 * - 0x2C77 - __le3278 - s_mtime79 - Mount time, in seconds since the epoch.80 * - 0x3081 - __le3282 - s_wtime83 - Write time, in seconds since the epoch.84 * - 0x3485 - __le1686 - s_mnt_count87 - Number of mounts since the last fsck.88 * - 0x3689 - __le1690 - s_max_mnt_count91 - Number of mounts beyond which a fsck is needed.92 * - 0x3893 - __le1694 - s_magic95 - Magic signature, 0xEF5396 * - 0x3A97 - __le1698 - s_state99 - File system state. See super_state_ for more info.100 * - 0x3C101 - __le16102 - s_errors103 - Behaviour when detecting errors. See super_errors_ for more info.104 * - 0x3E105 - __le16106 - s_minor_rev_level107 - Minor revision level.108 * - 0x40109 - __le32110 - s_lastcheck111 - Time of last check, in seconds since the epoch.112 * - 0x44113 - __le32114 - s_checkinterval115 - Maximum time between checks, in seconds.116 * - 0x48117 - __le32118 - s_creator_os119 - Creator OS. See the table super_creator_ for more info.120 * - 0x4C121 - __le32122 - s_rev_level123 - Revision level. See the table super_revision_ for more info.124 * - 0x50125 - __le16126 - s_def_resuid127 - Default uid for reserved blocks.128 * - 0x52129 - __le16130 - s_def_resgid131 - Default gid for reserved blocks.132 * -133 -134 -135 - These fields are for EXT4_DYNAMIC_REV superblocks only.136 137 Note: the difference between the compatible feature set and the138 incompatible feature set is that if there is a bit set in the139 incompatible feature set that the kernel doesn't know about, it should140 refuse to mount the filesystem.141 142 e2fsck's requirements are more strict; if it doesn't know143 about a feature in either the compatible or incompatible feature set, it144 must abort and not try to meddle with things it doesn't understand...145 * - 0x54146 - __le32147 - s_first_ino148 - First non-reserved inode.149 * - 0x58150 - __le16151 - s_inode_size152 - Size of inode structure, in bytes.153 * - 0x5A154 - __le16155 - s_block_group_nr156 - Block group # of this superblock.157 * - 0x5C158 - __le32159 - s_feature_compat160 - Compatible feature set flags. Kernel can still read/write this fs even161 if it doesn't understand a flag; fsck should not do that. See the162 super_compat_ table for more info.163 * - 0x60164 - __le32165 - s_feature_incompat166 - Incompatible feature set. If the kernel or fsck doesn't understand one167 of these bits, it should stop. See the super_incompat_ table for more168 info.169 * - 0x64170 - __le32171 - s_feature_ro_compat172 - Readonly-compatible feature set. If the kernel doesn't understand one of173 these bits, it can still mount read-only. See the super_rocompat_ table174 for more info.175 * - 0x68176 - __u8177 - s_uuid[16]178 - 128-bit UUID for volume.179 * - 0x78180 - char181 - s_volume_name[16]182 - Volume label.183 * - 0x88184 - char185 - s_last_mounted[64]186 - Directory where filesystem was last mounted.187 * - 0xC8188 - __le32189 - s_algorithm_usage_bitmap190 - For compression (Not used in e2fsprogs/Linux)191 * -192 -193 -194 - Performance hints. Directory preallocation should only happen if the195 EXT4_FEATURE_COMPAT_DIR_PREALLOC flag is on.196 * - 0xCC197 - __u8198 - s_prealloc_blocks199 - #. of blocks to try to preallocate for ... files? (Not used in200 e2fsprogs/Linux)201 * - 0xCD202 - __u8203 - s_prealloc_dir_blocks204 - #. of blocks to preallocate for directories. (Not used in205 e2fsprogs/Linux)206 * - 0xCE207 - __le16208 - s_reserved_gdt_blocks209 - Number of reserved GDT entries for future filesystem expansion.210 * -211 -212 -213 - Journalling support is valid only if EXT4_FEATURE_COMPAT_HAS_JOURNAL is214 set.215 * - 0xD0216 - __u8217 - s_journal_uuid[16]218 - UUID of journal superblock219 * - 0xE0220 - __le32221 - s_journal_inum222 - inode number of journal file.223 * - 0xE4224 - __le32225 - s_journal_dev226 - Device number of journal file, if the external journal feature flag is227 set.228 * - 0xE8229 - __le32230 - s_last_orphan231 - Start of list of orphaned inodes to delete.232 * - 0xEC233 - __le32234 - s_hash_seed[4]235 - HTREE hash seed.236 * - 0xFC237 - __u8238 - s_def_hash_version239 - Default hash algorithm to use for directory hashes. See super_def_hash_240 for more info.241 * - 0xFD242 - __u8243 - s_jnl_backup_type244 - If this value is 0 or EXT3_JNL_BACKUP_BLOCKS (1), then the245 ``s_jnl_blocks`` field contains a duplicate copy of the inode's246 ``i_block[]`` array and ``i_size``.247 * - 0xFE248 - __le16249 - s_desc_size250 - Size of group descriptors, in bytes, if the 64bit incompat feature flag251 is set.252 * - 0x100253 - __le32254 - s_default_mount_opts255 - Default mount options. See the super_mountopts_ table for more info.256 * - 0x104257 - __le32258 - s_first_meta_bg259 - First metablock block group, if the meta_bg feature is enabled.260 * - 0x108261 - __le32262 - s_mkfs_time263 - When the filesystem was created, in seconds since the epoch.264 * - 0x10C265 - __le32266 - s_jnl_blocks[17]267 - Backup copy of the journal inode's ``i_block[]`` array in the first 15268 elements and i_size_high and i_size in the 16th and 17th elements,269 respectively.270 * -271 -272 -273 - 64bit support is valid only if EXT4_FEATURE_COMPAT_64BIT is set.274 * - 0x150275 - __le32276 - s_blocks_count_hi277 - High 32-bits of the block count.278 * - 0x154279 - __le32280 - s_r_blocks_count_hi281 - High 32-bits of the reserved block count.282 * - 0x158283 - __le32284 - s_free_blocks_count_hi285 - High 32-bits of the free block count.286 * - 0x15C287 - __le16288 - s_min_extra_isize289 - All inodes have at least # bytes.290 * - 0x15E291 - __le16292 - s_want_extra_isize293 - New inodes should reserve # bytes.294 * - 0x160295 - __le32296 - s_flags297 - Miscellaneous flags. See the super_flags_ table for more info.298 * - 0x164299 - __le16300 - s_raid_stride301 - RAID stride. This is the number of logical blocks read from or written302 to the disk before moving to the next disk. This affects the placement303 of filesystem metadata, which will hopefully make RAID storage faster.304 * - 0x166305 - __le16306 - s_mmp_interval307 - #. seconds to wait in multi-mount prevention (MMP) checking. In theory,308 MMP is a mechanism to record in the superblock which host and device309 have mounted the filesystem, in order to prevent multiple mounts. This310 feature does not seem to be implemented...311 * - 0x168312 - __le64313 - s_mmp_block314 - Block # for multi-mount protection data.315 * - 0x170316 - __le32317 - s_raid_stripe_width318 - RAID stripe width. This is the number of logical blocks read from or319 written to the disk before coming back to the current disk. This is used320 by the block allocator to try to reduce the number of read-modify-write321 operations in a RAID5/6.322 * - 0x174323 - __u8324 - s_log_groups_per_flex325 - Size of a flexible block group is 2 ^ ``s_log_groups_per_flex``.326 * - 0x175327 - __u8328 - s_checksum_type329 - Metadata checksum algorithm type. The only valid value is 1 (crc32c).330 * - 0x176331 - __le16332 - s_reserved_pad333 -334 * - 0x178335 - __le64336 - s_kbytes_written337 - Number of KiB written to this filesystem over its lifetime.338 * - 0x180339 - __le32340 - s_snapshot_inum341 - inode number of active snapshot. (Not used in e2fsprogs/Linux.)342 * - 0x184343 - __le32344 - s_snapshot_id345 - Sequential ID of active snapshot. (Not used in e2fsprogs/Linux.)346 * - 0x188347 - __le64348 - s_snapshot_r_blocks_count349 - Number of blocks reserved for active snapshot's future use. (Not used in350 e2fsprogs/Linux.)351 * - 0x190352 - __le32353 - s_snapshot_list354 - inode number of the head of the on-disk snapshot list. (Not used in355 e2fsprogs/Linux.)356 * - 0x194357 - __le32358 - s_error_count359 - Number of errors seen.360 * - 0x198361 - __le32362 - s_first_error_time363 - First time an error happened, in seconds since the epoch.364 * - 0x19C365 - __le32366 - s_first_error_ino367 - inode involved in first error.368 * - 0x1A0369 - __le64370 - s_first_error_block371 - Number of block involved of first error.372 * - 0x1A8373 - __u8374 - s_first_error_func[32]375 - Name of function where the error happened.376 * - 0x1C8377 - __le32378 - s_first_error_line379 - Line number where error happened.380 * - 0x1CC381 - __le32382 - s_last_error_time383 - Time of most recent error, in seconds since the epoch.384 * - 0x1D0385 - __le32386 - s_last_error_ino387 - inode involved in most recent error.388 * - 0x1D4389 - __le32390 - s_last_error_line391 - Line number where most recent error happened.392 * - 0x1D8393 - __le64394 - s_last_error_block395 - Number of block involved in most recent error.396 * - 0x1E0397 - __u8398 - s_last_error_func[32]399 - Name of function where the most recent error happened.400 * - 0x200401 - __u8402 - s_mount_opts[64]403 - ASCIIZ string of mount options.404 * - 0x240405 - __le32406 - s_usr_quota_inum407 - Inode number of user `quota <quota>`__ file.408 * - 0x244409 - __le32410 - s_grp_quota_inum411 - Inode number of group `quota <quota>`__ file.412 * - 0x248413 - __le32414 - s_overhead_blocks415 - Overhead blocks/clusters in fs. (Huh? This field is always zero, which416 means that the kernel calculates it dynamically.)417 * - 0x24C418 - __le32419 - s_backup_bgs[2]420 - Block groups containing superblock backups (if sparse_super2)421 * - 0x254422 - __u8423 - s_encrypt_algos[4]424 - Encryption algorithms in use. There can be up to four algorithms in use425 at any time; valid algorithm codes are given in the super_encrypt_ table426 below.427 * - 0x258428 - __u8429 - s_encrypt_pw_salt[16]430 - Salt for the string2key algorithm for encryption.431 * - 0x268432 - __le32433 - s_lpf_ino434 - Inode number of lost+found435 * - 0x26C436 - __le32437 - s_prj_quota_inum438 - Inode that tracks project quotas.439 * - 0x270440 - __le32441 - s_checksum_seed442 - Checksum seed used for metadata_csum calculations. This value is443 crc32c(~0, $orig_fs_uuid).444 * - 0x274445 - __u8446 - s_wtime_hi447 - Upper 8 bits of the s_wtime field.448 * - 0x275449 - __u8450 - s_mtime_hi451 - Upper 8 bits of the s_mtime field.452 * - 0x276453 - __u8454 - s_mkfs_time_hi455 - Upper 8 bits of the s_mkfs_time field.456 * - 0x277457 - __u8458 - s_lastcheck_hi459 - Upper 8 bits of the s_lastcheck field.460 * - 0x278461 - __u8462 - s_first_error_time_hi463 - Upper 8 bits of the s_first_error_time field.464 * - 0x279465 - __u8466 - s_last_error_time_hi467 - Upper 8 bits of the s_last_error_time field.468 * - 0x27A469 - __u8470 - s_pad[2]471 - Zero padding.472 * - 0x27C473 - __le16474 - s_encoding475 - Filename charset encoding.476 * - 0x27E477 - __le16478 - s_encoding_flags479 - Filename charset encoding flags.480 * - 0x280481 - __le32482 - s_orphan_file_inum483 - Orphan file inode number.484 * - 0x284485 - __le32486 - s_reserved[94]487 - Padding to the end of the block.488 * - 0x3FC489 - __le32490 - s_checksum491 - Superblock checksum.492 493.. _super_state:494 495The superblock state is some combination of the following:496 497.. list-table::498 :widths: 8 72499 :header-rows: 1500 501 * - Value502 - Description503 * - 0x0001504 - Cleanly umounted505 * - 0x0002506 - Errors detected507 * - 0x0004508 - Orphans being recovered509 510.. _super_errors:511 512The superblock error policy is one of the following:513 514.. list-table::515 :widths: 8 72516 :header-rows: 1517 518 * - Value519 - Description520 * - 1521 - Continue522 * - 2523 - Remount read-only524 * - 3525 - Panic526 527.. _super_creator:528 529The filesystem creator is one of the following:530 531.. list-table::532 :widths: 8 72533 :header-rows: 1534 535 * - Value536 - Description537 * - 0538 - Linux539 * - 1540 - Hurd541 * - 2542 - Masix543 * - 3544 - FreeBSD545 * - 4546 - Lites547 548.. _super_revision:549 550The superblock revision is one of the following:551 552.. list-table::553 :widths: 8 72554 :header-rows: 1555 556 * - Value557 - Description558 * - 0559 - Original format560 * - 1561 - v2 format w/ dynamic inode sizes562 563Note that ``EXT4_DYNAMIC_REV`` refers to a revision 1 or newer filesystem.564 565.. _super_compat:566 567The superblock compatible features field is a combination of any of the568following:569 570.. list-table::571 :widths: 16 64572 :header-rows: 1573 574 * - Value575 - Description576 * - 0x1577 - Directory preallocation (COMPAT_DIR_PREALLOC).578 * - 0x2579 - “imagic inodes”. Not clear from the code what this does580 (COMPAT_IMAGIC_INODES).581 * - 0x4582 - Has a journal (COMPAT_HAS_JOURNAL).583 * - 0x8584 - Supports extended attributes (COMPAT_EXT_ATTR).585 * - 0x10586 - Has reserved GDT blocks for filesystem expansion587 (COMPAT_RESIZE_INODE). Requires RO_COMPAT_SPARSE_SUPER.588 * - 0x20589 - Has directory indices (COMPAT_DIR_INDEX).590 * - 0x40591 - “Lazy BG”. Not in Linux kernel, seems to have been for uninitialized592 block groups? (COMPAT_LAZY_BG)593 * - 0x80594 - “Exclude inode”. Not used. (COMPAT_EXCLUDE_INODE).595 * - 0x100596 - “Exclude bitmap”. Seems to be used to indicate the presence of597 snapshot-related exclude bitmaps? Not defined in kernel or used in598 e2fsprogs (COMPAT_EXCLUDE_BITMAP).599 * - 0x200600 - Sparse Super Block, v2. If this flag is set, the SB field s_backup_bgs601 points to the two block groups that contain backup superblocks602 (COMPAT_SPARSE_SUPER2).603 * - 0x400604 - Fast commits supported. Although fast commits blocks are605 backward incompatible, fast commit blocks are not always606 present in the journal. If fast commit blocks are present in607 the journal, JBD2 incompat feature608 (JBD2_FEATURE_INCOMPAT_FAST_COMMIT) gets609 set (COMPAT_FAST_COMMIT).610 * - 0x1000611 - Orphan file allocated. This is the special file for more efficient612 tracking of unlinked but still open inodes. When there may be any613 entries in the file, we additionally set proper rocompat feature614 (RO_COMPAT_ORPHAN_PRESENT).615 616.. _super_incompat:617 618The superblock incompatible features field is a combination of any of the619following:620 621.. list-table::622 :widths: 16 64623 :header-rows: 1624 625 * - Value626 - Description627 * - 0x1628 - Compression (INCOMPAT_COMPRESSION).629 * - 0x2630 - Directory entries record the file type. See ext4_dir_entry_2 below631 (INCOMPAT_FILETYPE).632 * - 0x4633 - Filesystem needs recovery (INCOMPAT_RECOVER).634 * - 0x8635 - Filesystem has a separate journal device (INCOMPAT_JOURNAL_DEV).636 * - 0x10637 - Meta block groups. See the earlier discussion of this feature638 (INCOMPAT_META_BG).639 * - 0x40640 - Files in this filesystem use extents (INCOMPAT_EXTENTS).641 * - 0x80642 - Enable a filesystem size of 2^64 blocks (INCOMPAT_64BIT).643 * - 0x100644 - Multiple mount protection (INCOMPAT_MMP).645 * - 0x200646 - Flexible block groups. See the earlier discussion of this feature647 (INCOMPAT_FLEX_BG).648 * - 0x400649 - Inodes can be used to store large extended attribute values650 (INCOMPAT_EA_INODE).651 * - 0x1000652 - Data in directory entry (INCOMPAT_DIRDATA). (Not implemented?)653 * - 0x2000654 - Metadata checksum seed is stored in the superblock. This feature enables655 the administrator to change the UUID of a metadata_csum filesystem656 while the filesystem is mounted; without it, the checksum definition657 requires all metadata blocks to be rewritten (INCOMPAT_CSUM_SEED).658 * - 0x4000659 - Large directory >2GB or 3-level htree (INCOMPAT_LARGEDIR). Prior to660 this feature, directories could not be larger than 4GiB and could not661 have an htree more than 2 levels deep. If this feature is enabled,662 directories can be larger than 4GiB and have a maximum htree depth of 3.663 * - 0x8000664 - Data in inode (INCOMPAT_INLINE_DATA).665 * - 0x10000666 - Encrypted inodes are present on the filesystem. (INCOMPAT_ENCRYPT).667 668.. _super_rocompat:669 670The superblock read-only compatible features field is a combination of any of671the following:672 673.. list-table::674 :widths: 16 64675 :header-rows: 1676 677 * - Value678 - Description679 * - 0x1680 - Sparse superblocks. See the earlier discussion of this feature681 (RO_COMPAT_SPARSE_SUPER).682 * - 0x2683 - This filesystem has been used to store a file greater than 2GiB684 (RO_COMPAT_LARGE_FILE).685 * - 0x4686 - Not used in kernel or e2fsprogs (RO_COMPAT_BTREE_DIR).687 * - 0x8688 - This filesystem has files whose sizes are represented in units of689 logical blocks, not 512-byte sectors. This implies a very large file690 indeed! (RO_COMPAT_HUGE_FILE)691 * - 0x10692 - Group descriptors have checksums. In addition to detecting corruption,693 this is useful for lazy formatting with uninitialized groups694 (RO_COMPAT_GDT_CSUM).695 * - 0x20696 - Indicates that the old ext3 32,000 subdirectory limit no longer applies697 (RO_COMPAT_DIR_NLINK). A directory's i_links_count will be set to 1698 if it is incremented past 64,999.699 * - 0x40700 - Indicates that large inodes exist on this filesystem701 (RO_COMPAT_EXTRA_ISIZE).702 * - 0x80703 - This filesystem has a snapshot (RO_COMPAT_HAS_SNAPSHOT).704 * - 0x100705 - `Quota <Quota>`__ (RO_COMPAT_QUOTA).706 * - 0x200707 - This filesystem supports “bigalloc”, which means that file extents are708 tracked in units of clusters (of blocks) instead of blocks709 (RO_COMPAT_BIGALLOC).710 * - 0x400711 - This filesystem supports metadata checksumming.712 (RO_COMPAT_METADATA_CSUM; implies RO_COMPAT_GDT_CSUM, though713 GDT_CSUM must not be set)714 * - 0x800715 - Filesystem supports replicas. This feature is neither in the kernel nor716 e2fsprogs. (RO_COMPAT_REPLICA)717 * - 0x1000718 - Read-only filesystem image; the kernel will not mount this image719 read-write and most tools will refuse to write to the image.720 (RO_COMPAT_READONLY)721 * - 0x2000722 - Filesystem tracks project quotas. (RO_COMPAT_PROJECT)723 * - 0x8000724 - Verity inodes may be present on the filesystem. (RO_COMPAT_VERITY)725 * - 0x10000726 - Indicates orphan file may have valid orphan entries and thus we need727 to clean them up when mounting the filesystem728 (RO_COMPAT_ORPHAN_PRESENT).729 730.. _super_def_hash:731 732The ``s_def_hash_version`` field is one of the following:733 734.. list-table::735 :widths: 8 72736 :header-rows: 1737 738 * - Value739 - Description740 * - 0x0741 - Legacy.742 * - 0x1743 - Half MD4.744 * - 0x2745 - Tea.746 * - 0x3747 - Legacy, unsigned.748 * - 0x4749 - Half MD4, unsigned.750 * - 0x5751 - Tea, unsigned.752 753.. _super_mountopts:754 755The ``s_default_mount_opts`` field is any combination of the following:756 757.. list-table::758 :widths: 8 72759 :header-rows: 1760 761 * - Value762 - Description763 * - 0x0001764 - Print debugging info upon (re)mount. (EXT4_DEFM_DEBUG)765 * - 0x0002766 - New files take the gid of the containing directory (instead of the fsgid767 of the current process). (EXT4_DEFM_BSDGROUPS)768 * - 0x0004769 - Support userspace-provided extended attributes. (EXT4_DEFM_XATTR_USER)770 * - 0x0008771 - Support POSIX access control lists (ACLs). (EXT4_DEFM_ACL)772 * - 0x0010773 - Do not support 32-bit UIDs. (EXT4_DEFM_UID16)774 * - 0x0020775 - All data and metadata are committed to the journal.776 (EXT4_DEFM_JMODE_DATA)777 * - 0x0040778 - All data are flushed to the disk before metadata are committed to the779 journal. (EXT4_DEFM_JMODE_ORDERED)780 * - 0x0060781 - Data ordering is not preserved; data may be written after the metadata782 has been written. (EXT4_DEFM_JMODE_WBACK)783 * - 0x0100784 - Disable write flushes. (EXT4_DEFM_NOBARRIER)785 * - 0x0200786 - Track which blocks in a filesystem are metadata and therefore should not787 be used as data blocks. This option will be enabled by default on 3.18,788 hopefully. (EXT4_DEFM_BLOCK_VALIDITY)789 * - 0x0400790 - Enable DISCARD support, where the storage device is told about blocks791 becoming unused. (EXT4_DEFM_DISCARD)792 * - 0x0800793 - Disable delayed allocation. (EXT4_DEFM_NODELALLOC)794 795.. _super_flags:796 797The ``s_flags`` field is any combination of the following:798 799.. list-table::800 :widths: 8 72801 :header-rows: 1802 803 * - Value804 - Description805 * - 0x0001806 - Signed directory hash in use.807 * - 0x0002808 - Unsigned directory hash in use.809 * - 0x0004810 - To test development code.811 812.. _super_encrypt:813 814The ``s_encrypt_algos`` list can contain any of the following:815 816.. list-table::817 :widths: 8 72818 :header-rows: 1819 820 * - Value821 - Description822 * - 0823 - Invalid algorithm (ENCRYPTION_MODE_INVALID).824 * - 1825 - 256-bit AES in XTS mode (ENCRYPTION_MODE_AES_256_XTS).826 * - 2827 - 256-bit AES in GCM mode (ENCRYPTION_MODE_AES_256_GCM).828 * - 3829 - 256-bit AES in CBC mode (ENCRYPTION_MODE_AES_256_CBC).830 831Total size of the superblock is 1024 bytes.832