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docs/erasure/README.md
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docs/erasure/README.md
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# MinIO Erasure Code Quickstart Guide [](https://slack.min.io)
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MinIO protects data against hardware failures and silent data corruption using erasure code and checksums. With the highest level of redundancy, you may lose up to half (N/2) of the total drives and still be able to recover the data.
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## What is Erasure Code?
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Erasure code is a mathematical algorithm to reconstruct missing or corrupted data. MinIO uses Reed-Solomon code to shard objects into variable data and parity blocks. For example, in a 12 drive setup, an object can be sharded to a variable number of data and parity blocks across all the drives - ranging from six data and six parity blocks to ten data and two parity blocks.
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By default, MinIO shards the objects across N/2 data and N/2 parity drives. Though, you can use [storage classes](https://github.com/minio/minio/tree/master/docs/erasure/storage-class) to use a custom configuration. We recommend N/2 data and parity blocks, as it ensures the best protection from drive failures.
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In 12 drive example above, with MinIO server running in the default configuration, you can lose any of the six drives and still reconstruct the data reliably from the remaining drives.
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## Why is Erasure Code useful?
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Erasure code protects data from multiple drives failure, unlike RAID or replication. For example, RAID6 can protect against two drive failure whereas in MinIO erasure code you can lose as many as half of drives and still the data remains safe. Further, MinIO's erasure code is at the object level and can heal one object at a time. For RAID, healing can be done only at the volume level which translates into high downtime. As MinIO encodes each object individually, it can heal objects incrementally. Storage servers once deployed should not require drive replacement or healing for the lifetime of the server. MinIO's erasure coded backend is designed for operational efficiency and takes full advantage of hardware acceleration whenever available.
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## What is Bit Rot protection?
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Bit Rot, also known as data rot or silent data corruption is a data loss issue faced by disk drives today. Data on the drive may silently get corrupted without signaling an error has occurred, making bit rot more dangerous than a permanent hard drive failure.
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MinIO's erasure coded backend uses high speed [HighwayHash](https://github.com/minio/highwayhash) checksums to protect against Bit Rot.
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## How are drives used for Erasure Code?
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MinIO divides the drives you provide into erasure-coding sets of *2 to 16* drives. Therefore, the number of drives you present must be a multiple of one of these numbers. Each object is written to a single erasure-coding set.
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Minio uses the largest possible EC set size which divides into the number of drives given. For example, *18 drives* are configured as *2 sets of 9 drives*, and *24 drives* are configured as *2 sets of 12 drives*. This is true for scenarios when running MinIO as a standalone erasure coded deployment. In [distributed setup however node (affinity) based](https://docs.min.io/community/minio-object-store/operations/install-deploy-manage/deploy-minio-multi-node-multi-drive.html) erasure stripe sizes are chosen.
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The drives should all be of approximately the same size.
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## Get Started with MinIO in Erasure Code
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### 1. Prerequisites
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Install MinIO - [MinIO Quickstart Guide](https://docs.min.io/community/minio-object-store/operations/deployments/baremetal-deploy-minio-on-redhat-linux.html)
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### 2. Run MinIO Server with Erasure Code
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Example: Start MinIO server in a 12 drives setup, using MinIO binary.
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```sh
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minio server /data{1...12}
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```
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Example: Start MinIO server in a 8 drives setup, using MinIO Docker image.
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```sh
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podman run \
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-p 9000:9000 \
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-p 9001:9001 \
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--name minio \
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-v /mnt/data1:/data1 \
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-v /mnt/data2:/data2 \
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-v /mnt/data3:/data3 \
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-v /mnt/data4:/data4 \
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-v /mnt/data5:/data5 \
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-v /mnt/data6:/data6 \
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-v /mnt/data7:/data7 \
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-v /mnt/data8:/data8 \
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quay.io/minio/minio server /data{1...8} --console-address ":9001"
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```
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### 3. Test your setup
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You may unplug drives randomly and continue to perform I/O on the system.
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docs/erasure/storage-class/README.md
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docs/erasure/storage-class/README.md
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# MinIO Storage Class Quickstart Guide [](https://slack.min.io)
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MinIO server supports storage class in erasure coding mode. This allows configurable data and parity drives per object.
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This page is intended as a summary of MinIO Erasure Coding. For a more complete explanation, see <https://docs.min.io/community/minio-object-store/operations/concepts/erasure-coding.html>.
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## Overview
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MinIO supports two storage classes, Reduced Redundancy class and Standard class. These classes can be defined using environment variables
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set before starting MinIO server. After the data and parity drives for each storage class are defined using environment variables,
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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
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saving the object in specific number of data and parity drives.
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## Storage usage
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The selection of varying data and parity drives has a direct impact on the drive space usage. With storage class, you can optimize for high
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redundancy or better drive space utilization.
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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
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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
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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
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two parity drives, 100 MiB file takes only approximately 114 MiB.
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Below is a list of data/parity drives and corresponding _approximate_ storage space usage on a 16 drive MinIO deployment. The field _storage
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usage ratio_ is simply the drive space used by the file after erasure-encoding, divided by actual file size.
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| Total Drives (N) | Data Drives (D) | Parity Drives (P) | Storage Usage Ratio |
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|------------------|-----------------|-------------------|---------------------|
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| 16 | 8 | 8 | 2.00 |
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| 16 | 9 | 7 | 1.79 |
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| 16 | 10 | 6 | 1.60 |
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| 16 | 11 | 5 | 1.45 |
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| 16 | 12 | 4 | 1.34 |
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| 16 | 13 | 3 | 1.23 |
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| 16 | 14 | 2 | 1.14 |
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You can calculate _approximate_ storage usage ratio using the formula - total drives (N) / data drives (D).
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### Allowed values for STANDARD storage class
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`STANDARD` storage class implies more parity than `REDUCED_REDUNDANCY` class. So, `STANDARD` parity drives should be
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- Greater than or equal to 2, if `REDUCED_REDUNDANCY` parity is not set.
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- Greater than `REDUCED_REDUNDANCY` parity, if it is set.
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Parity blocks can not be higher than data blocks, so `STANDARD` storage class parity can not be higher than N/2. (N being total number of drives)
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The default value for the `STANDARD` storage class depends on the number of volumes in the erasure set:
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| Erasure Set Size | Default Parity (EC:N) |
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|------------------|-----------------------|
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| 5 or fewer | EC:2 |
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| 6-7 | EC:3 |
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| 8 or more | EC:4 |
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For more complete documentation on Erasure Set sizing, see the [MinIO Documentation on Erasure Sets](https://docs.min.io/community/minio-object-store/operations/concepts/erasure-coding.html#erasure-sets).
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### Allowed values for REDUCED_REDUNDANCY storage class
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`REDUCED_REDUNDANCY` implies lesser parity than `STANDARD` class. So,`REDUCED_REDUNDANCY` parity drives should be
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- Less than N/2, if `STANDARD` parity is not set.
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- Less than `STANDARD` Parity, if it is set.
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Default value for `REDUCED_REDUNDANCY` storage class is `1`.
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## Get started with Storage Class
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### Set storage class
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The format to set storage class environment variables is as follows
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`MINIO_STORAGE_CLASS_STANDARD=EC:parity`
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`MINIO_STORAGE_CLASS_RRS=EC:parity`
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For example, set `MINIO_STORAGE_CLASS_RRS` parity 2 and `MINIO_STORAGE_CLASS_STANDARD` parity 3
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```sh
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export MINIO_STORAGE_CLASS_STANDARD=EC:3
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export MINIO_STORAGE_CLASS_RRS=EC:2
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```
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Storage class can also be set via `mc admin config` get/set commands to update the configuration. Refer [storage class](https://github.com/minio/minio/tree/master/docs/config#storage-class) for
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more details.
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#### Note
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- If `STANDARD` storage class is set via environment variables or `mc admin config` get/set commands, and `x-amz-storage-class` is not present in request metadata, MinIO server will
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apply `STANDARD` storage class to the object. This means the data and parity drives will be used as set in `STANDARD` storage class.
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- If storage class is not defined before starting MinIO server, and subsequent PutObject metadata field has `x-amz-storage-class` present
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with values `REDUCED_REDUNDANCY` or `STANDARD`, MinIO server uses default parity values.
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### Set metadata
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In below example `minio-go` is used to set the storage class to `REDUCED_REDUNDANCY`. This means this object will be split across 6 data drives and 2 parity drives (as per the storage class set in previous step).
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```go
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s3Client, err := minio.New("localhost:9000", "YOUR-ACCESSKEYID", "YOUR-SECRETACCESSKEY", true)
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if err != nil {
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log.Fatalln(err)
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}
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object, err := os.Open("my-testfile")
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if err != nil {
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log.Fatalln(err)
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}
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defer object.Close()
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objectStat, err := object.Stat()
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if err != nil {
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log.Fatalln(err)
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}
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n, err := s3Client.PutObject("my-bucketname", "my-objectname", object, objectStat.Size(), minio.PutObjectOptions{ContentType: "application/octet-stream", StorageClass: "REDUCED_REDUNDANCY"})
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if err != nil {
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log.Fatalln(err)
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}
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log.Println("Uploaded", "my-objectname", " of size: ", n, "Successfully.")
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```
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