29.2. System Requirements
- The VDO module requires 370 MB plus an additional 268 MB per each 1 TB of physical storage managed.
- The Universal Deduplication Service (UDS) index requires a minimum of 250 MB of DRAM, which is also the default amount that deduplication uses. For details on the memory usage of UDS, see Section 29.2.1, “UDS Index Memory Requirements”.
Additional System Software
- Python 2.7
yumpackage manager will install all necessary software dependencies automatically.
Placement of VDO in the Storage Stack
- Under VDO: DM-Multipath, DM-Crypt, and software RAID (LVM or
- On top of VDO: LVM cache, LVM snapshots, and LVM Thin Provisioning.
- VDO on top of VDO volumes: storage → VDO → LVM → VDO
- VDO on top of LVM Snapshots
- VDO on top of LVM Cache
- VDO on top of the loopback device
- VDO on top of LVM Thin Provisioning
- Encrypted volumes on top of VDO: storage → VDO → DM-Crypt
- Partitions on a VDO volume:
parted, and similar partitions
- RAID (LVM, MD, or any other type) on top of a VDO volume
async. When VDO is in
syncmode, writes to the VDO device are acknowledged when the underlying storage has written the data permanently. When VDO is in
asyncmode, writes are acknowledged before being written to persistent storage.
autooption, which selects the appropriate policy automatically.
29.2.1. UDS Index Memory Requirements
- A compact representation is used in memory that contains at most one entry per unique block.
- An on-disk component which records the associated block names presented to the index as they occur, in order.
- For a dense index, UDS will provide a deduplication window of 1 TB per 1 GB of RAM. A 1 GB index is generally sufficient for storage systems of up to 4 TB.
- For a sparse index, UDS will provide a deduplication window of 10 TB per 1 GB of RAM. A 1 GB sparse index is generally sufficient for up to 40 TB of physical storage.
29.2.2. VDO Storage Space Requirements
- VDO writes two types of metadata to its underlying physical storage:
See Section 29.1.3, “VDO Volume” for a description of slabs.
- The first type scales with the physical size of the VDO volume and uses approximately 1 MB for each 4 GB of physical storage plus an additional 1 MB per slab.
- The second type scales with the logical size of the VDO volume and consumes approximately 1.25 MB for each 1 GB of logical storage, rounded up to the nearest slab.
- The UDS index is stored within the VDO volume group and is managed by the associated VDO instance. The amount of storage required depends on the type of index and the amount of RAM allocated to the index. For each 1 GB of RAM, a dense UDS index will use 17 GB of storage, and a sparse UDS index will use 170 GB of storage.
29.2.3. Examples of VDO System Requirements by Physical Volume Size
Primary Storage Deployment
Table 29.2. VDO Storage and Memory Requirements for Primary Storage
|Physical Volume Size||10 GB – 1–TB||2–10 TB||11–50 TB||51–100 TB||101–256 TB|
|RAM Usage||250 MB|| |
Dense: 1 GB
Sparse: 250 MB
|2 GB||3 GB||12 GB|
|Disk Usage||2.5 GB|| |
Dense: 10 GB
Sparse: 22 GB
|170 GB||255 GB||1020 GB|
|Index Type||Dense||Dense or Sparse||Sparse||Sparse||Sparse|
Backup Storage Deployment
Table 29.3. VDO Storage and Memory Requirements for Backup Storage
|Physical Volume Size||10 GB – 1 TB||2–10 TB||11–50 TB||51–100 TB||101–256 TB|
|RAM Usage||250 MB||2 GB||10 GB||20 GB||26 GB|
|Disk Usage||2.5 GB||170 GB||850 GB||1700 GB||3400 GB|