Disk sizing for heavy write scenarios

Sizing considerations for persistent disk space for heavy throughput databases.

In extreme write scenarios when append-only files (AOF) are enabled, the AOF rewrite process can require considerably more disk space for database persistence.

For disk size requirements for standard usage, see Hardware requirements.

Estimate required disk space

To estimate the required persistent disk space for AOF rewrite purposes in extreme write scenarios, use the following formula:

X (1 + 3Y + Y²)

Where:

• X = size of each shard in GB
• Y = number of shards

Examples

The following examples show how to calculate the persistent disk space required for heavy write scenarios for different database configurations, where:

• Database size is the memory limit configured for the database.

• Number of shards is the total number of shards (primary shards + replica shards).

Example 1

• Database size = 10 GB
• Number of shards = 4

1. Calculate the shard size:

   Shard size = database size / number of shards
              = 10 GB / 4 shards
              = 2.5 GB per shard
   

2. Use the formula to calculate the required persistent disk space:

   Disk space = X (1 + 3Y + Y²)
              = 2.5 (1 + 3 × 4 + 4²)
              = 2.5 (1 + 12 + 16)
              = 2.5 × 29
              = 72.5 GB
   

3. Round up to 73 GB of required disk space.

Example 2

• Database size = 10 GB
• Number of shards = 16

1. Calculate the shard size:

   Shard size = database size / number of shards
              = 10 GB / 16 shards
              = 0.625 GB per shard
   

2. Use the formula to calculate the required persistent disk space:

   Disk space = X (1 + 3Y + Y²)
              = 0.625 (1 + 3 × 16 + 16²)
              = 0.625 (1 + 48 + 256)
              = 0.625 × 305
              = 190.625 GB
   

3. Round up to 191 GB of required disk space.

Example 3

• Database size = 40 GB
• Number of shards = 5

1. Calculate the shard size:

   Shard size = database size / number of shards
              = 40 GB / 5 shards
              = 8 GB per shard
   

2. Use the formula to calculate the required persistent disk space:

   Disk space = X (1 + 3Y + Y²)
              = 8 (1 + 3 × 5 + 5²)
              = 8 (1 + 15 + 25)
              = 8 × 41
              = 328 GB
   

3. Required disk space: 328 GB.

Example 4

• Database size = 40 GB
• Number of shards = 15

1. Calculate the shard size:

   Shard size = database size / number of shards
              = 40 GB / 15 shards
              = 2.67 GB per shard
   

2. Use the formula to calculate the required persistent disk space:

   Disk space = X (1 + 3Y + Y²)
              = 2.67 (1 + 3 × 15 + 15²)
              = 2.67 (1 + 45 + 225)
              = 2.67 × 271
              = 723.57 GB
   

3. Round up to 724 GB of required disk space.