s3: update docs with a Reducing Costs section - Fixes #2889
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Nick Craig-Wood
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@ -248,25 +248,6 @@ d) Delete this remote
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y/e/d>
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```
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### --fast-list ###
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This remote supports `--fast-list` which allows you to use fewer
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transactions in exchange for more memory. See the [rclone
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docs](/docs/#fast-list) for more details.
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### --update and --use-server-modtime ###
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As noted below, the modified time is stored on metadata on the object. It is
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used by default for all operations that require checking the time a file was
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last updated. It allows rclone to treat the remote more like a true filesystem,
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but it is inefficient because it requires an extra API call to retrieve the
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metadata.
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For many operations, the time the object was last uploaded to the remote is
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sufficient to determine if it is "dirty". By using `--update` along with
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`--use-server-modtime`, you can avoid the extra API call and simply upload
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files whose local modtime is newer than the time it was last uploaded.
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### Modified time ###
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The modified time is stored as metadata on the object as
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@ -280,6 +261,87 @@ storage the object will be uploaded rather than copied.
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Note that reading this from the object takes an additional `HEAD`
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request as the metadata isn't returned in object listings.
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### Reducing costs
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#### Avoiding HEAD requests to read the modification time
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By default rclone will use the modification time of objects stored in
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S3 for syncing. This is stored in object metadata which unfortunately
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takes an extra HEAD request to read which can be expensive (in time
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and money).
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The modification time is used by default for all operations that
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require checking the time a file was last updated. It allows rclone to
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treat the remote more like a true filesystem, but it is inefficient on
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S3 because it requires an extra API call to retrieve the metadata.
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The extra API calls can be avoided when syncing (using `rclone sync`
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or `rclone copy`) in a few different ways, each with its own
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tradeoffs.
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- `--size-only`
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- Only checks the size of files.
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- Uses no extra transactions.
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- If the file doesn't change size then rclone won't detect it has
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changed.
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- `rclone sync --size-only /path/to/source s3:bucket`
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- `--checksum`
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- Checks the size and MD5 checksum of files.
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- Uses no extra transactions.
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- The most accurate detection of changes possible.
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- Will cause the source to read an MD5 checksum which, if it is a
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local disk, will cause lots of disk activity.
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- If the source and destination are both S3 this is the
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**recommended** flag to use for maximum efficiency.
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- `rclone sync --checksum /path/to/source s3:bucket`
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- `--update --use-server-modtime`
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- Uses no extra transactions.
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- Modification time becomes the time the object was uploaded.
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- For many operations this is sufficient to determine if it needs
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uploading.
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- Using `--update` along with `--use-server-modtime`, avoids the
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extra API call and uploads files whose local modification time
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is newer than the time it was last uploaded.
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- Files created with timestamps in the past will be missed by the sync.
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- `rclone sync --update --use-server-modtime /path/to/source s3:bucket`
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These flags can and should be used in combination with `--fast-list` -
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see below.
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If using `rclone mount` or any command using the VFS (eg `rclone
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serve`) commands then you might want to consider using the VFS flag
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`--no-modtime` which will stop rclone reading the modification time
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for every object. You could also use `--use-server-modtime` if you are
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happy with the modification times of the objects being the time of
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upload.
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#### Avoiding GET requests to read directory listings
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Rclone's default directory traversal is to process each directory
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individually. This takes one API call per directory. Using the
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`--fast-list` flag will read all info about the the objects into
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memory first using a smaller number of API calls (one per 1000
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objects). See the [rclone docs](/docs/#fast-list) for more details.
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rclone sync --fast-list --checksum /path/to/source s3:bucket
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`--fast-list` trades off API transactions for memory use. As a rough
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guide rclone uses 1k of memory per object stored, so using
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`--fast-list` on a sync of a million objects will use roughly 1 GB of
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RAM.
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If you are only copying a small number of files into a big repository
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then using `--no-traverse` is a good idea. This finds objects directly
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instead of through directory listings. You can do a "top-up" sync very
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cheaply by using `--max-age` and `--no-traverse` to copy only recent
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files, eg
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rclone copy --min-age 24h --no-traverse /path/to/source s3:bucket
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You'd then do a full `rclone sync` less often.
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Note that `--fast-list` isn't required in the top-up sync.
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### Hashes ###
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For small objects which weren't uploaded as multipart uploads (objects
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