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Update storage class related documents (#5399)

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- Add storage usage info in storage class doc
- Update distributed & erasure code doc with info on storage class
This commit is contained in:
Nitish Tiwari
2018-01-17 14:52:42 +05:30
committed by GitHub
parent 17301fe45d
commit 8a1dc10c60
3 changed files with 41 additions and 10 deletions
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29
docs/erasure/storage-class/README.md
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@@ -9,7 +9,32 @@ set before starting Minio server. After the data and parity disks for each stora
you can set the storage class of an object via request metadata field `x-amz-storage-class`. Minio server then honors the storage class by
saving the object in specific number of data and parity disks.
### Values for standard storage class (STANDARD)
## Storage usage
The selection of varying data and parity drives has a direct impact on the drive space usage. With storage class, you can optimise for high
redundancy or better drive space utilisation.
To get an idea of how various combinations of data and parity drives affect the storage usage, let’s take an example of a 100 MiB file stored
on 16 drive Minio deployment. If you use eight data and eight parity drives, the file space usage will be approximately twice, i.e. 100 MiB
file will take 200 MiB space. But, if you use ten data and six parity drives, same 100 MiB file takes around 160 MiB. If you use 14 data and
two parity drives, 100 MiB file takes only approximately 114 MiB.
Below is a list of data/parity drives and corresponding _approximate_ storage space usage on a 16 drive Minio deployment. The field _storage
usage ratio_ is simply the drive space used by the file after erasure-encoding, divided by actual file size.
| Total Drives (N) | Data Drives (D) | Parity Drives (P) | Storage Usage Ratio |
|------------------|-----------------|-------------------|---------------------|
| 16 | 8 | 8 | 2.00 |
| 16 | 9 | 7 | 1.79 |
| 16 | 10 | 6 | 1.60 |
| 16 | 11 | 5 | 1.45 |
| 16 | 12 | 4 | 1.34 |
| 16 | 13 | 3 | 1.23 |
| 16 | 14 | 2 | 1.14 |
You can calculate _approximate_ storage usage ratio using the formula - total drives (N) / data drives (D).
### Allowed values for STANDARD storage class
`STANDARD` storage class implies more parity than `REDUCED_REDUNDANCY` class. So, `STANDARD` parity disks should be
@@ -20,7 +45,7 @@ Parity blocks can not be higher than data blocks, so `STANDARD` storage class pa
Default value for `STANDARD` storage class is `N/2` (N is the total number of drives).
### Values for reduced redundancy storage class (REDUCED_REDUNDANCY)
### Allowed values for REDUCED_REDUNDANCY storage class
`REDUCED_REDUNDANCY` implies lesser parity than `STANDARD` class. So,`REDUCED_REDUNDANCY` parity disks should be