VBLK - Technical

Introduction

The VBLKs are the workhorse of the database. Each Disk Group, Disk, Volume, Partition and Component is represented by a group of VBLKs. The elements' relationships are shown in the Database Overview.

Each VBLK is 128 bytes long and has a standard 16 byte header. Sometimes the VBLK isn't large enough to store all the information, so the record will be fragmented across several VBLKs (which will have the same Group Number).

A table size of P implies the field is prefixed by a one byte length marker. Unless a string is listed as NULL terminated, it isn't.

Note to writers: there are 3 types of variable length integer fields:
1. Variable length UInt32 (length <= 4)
2. Variable length UInt64 (length <= 8)
3. Padded Variable length UInt64 (length <= 4 or length = 8)
for values not within the range of UInt32, this type must have a length prefix of 8. zeros should be added if necessary.

Standard VBLK Header

Every VBLK has a standard 16 byte header, containing accounting information.

Notes

The Sequence Numbers start at 4. 0 - 3 are effectively the VMDB Header block.

The Group Number of an occupied VBLK is never zero.

The Record Type can be 0x32 (Component), 0x33 (Partition), 0x34 / 0x44 (Disk), 0x35 / 0x45 (Disk Group) or 0x51 (Volume). Note that the first 4 bits denote the revision of the record, and the last 4 denote the type.

LBA values in extent / volume / component records refer to logical 512-byte blocks within the public region of the disk, regardless of the actual sector size of the disk. ("All disks holding extents for a given volume must have the same sector size").

Fragmented Records

The number of VBLK fragments is shown in Number of Fragments. Fragment Number is a zero-based index. To keep track of the record, each set is given a unique Group Number.

N.B. Fragmented VBLKs may not be located contiguously in the VMDB.

Update Status

To prevent data loss during updates, changes to the VBLKs are logged. In the event of a power failure, the database can be rolled back to a consistant state. The table below shows what each VBLK Update Status means.

Volume Record (0x51)

The record flags denote the presence of an optional field

N.B. Id1 and Id2 are mutually exclusive.

N.B. The optional fields will always be in the order: Id, Size, Mount Hint

Record Flags:

Volume Flags:

Read Policy:

Partition Type:

(a) Revision 5 of record type 1
(b) Volume Type: gen or raid5
(c) Volume State: ACTIVE or SYNC (for RAID 5)
(d) Initialized as 0xFFFFFFFF, Starts at 5 and unused numbers are reused
(e) length in bytes (this does not include VBLK headers)
(f) Disable driver letter assignment: 8000000000000000
(g) The ID of the object will be the Transaction ID that created this object
(h) Transaction ID of the last update

Component (0x32)

The record flags denote the presence of an optional field

Record Flags:

Component Flags:

Partition Layout:

(a) Revision 3 of record type 2
(b) Volume State: ACTIVE

Partition (0x33)

The record flags denote the presence of an optional field

Record Flags:

Partition Flags:

(a) Revision 3 of record type 3

Disk (0x34)

N.B. This record type doesn't have any flags

(a) Revision 3 of record type 4

Disk (0x44)

N.B. This record type doesn't have any flags

(a) Revision 4 of record type 4

Disk Flags:

Disk Group (0x35)

The record flags denote the presence of an optional field

(a) Revision 3 of record type 5
(b) Special values: 0xFFFFFFFF means 'all', 0 means 'default'.
(c) Default is 0

Disk Group (0x45)

The record flags denote the presence of an optional field

(a) Revision 4 of record type 5