11 KiB
| title | description | date |
|---|---|---|
| Cache | Rclone docs for cache remote | 2017-09-03 |
Cache (BETA)
The cache remote wraps another existing remote and stores file structure
and its data for long running tasks like rclone mount.
To get started you just need to have an existing remote which can be configured
with cache.
Here is an example of how to make a remote called test-cache. First run:
rclone config
This will guide you through an interactive setup process:
No remotes found - make a new one
n) New remote
r) Rename remote
c) Copy remote
s) Set configuration password
q) Quit config
n/r/c/s/q> n
name> test-cache
Type of storage to configure.
Choose a number from below, or type in your own value
...
5 / Cache a remote
\ "cache"
...
Storage> 5
Remote to cache.
Normally should contain a ':' and a path, eg "myremote:path/to/dir",
"myremote:bucket" or maybe "myremote:" (not recommended).
remote> local:/test
Optional: The URL of the Plex server
plex_url> http://127.0.0.1:32400
Optional: The username of the Plex user
plex_username> dummyusername
Optional: The password of the Plex user
y) Yes type in my own password
g) Generate random password
n) No leave this optional password blank
y/g/n> y
Enter the password:
password:
Confirm the password:
password:
The size of a chunk. Lower value good for slow connections but can affect seamless reading.
Default: 5M
Choose a number from below, or type in your own value
1 / 1MB
\ "1m"
2 / 5 MB
\ "5M"
3 / 10 MB
\ "10M"
chunk_size> 2
How much time should object info (file size, file hashes etc) be stored in cache. Use a very high value if you don't plan on changing the source FS from outside the cache.
Accepted units are: "s", "m", "h".
Default: 5m
Choose a number from below, or type in your own value
1 / 1 hour
\ "1h"
2 / 24 hours
\ "24h"
3 / 24 hours
\ "48h"
info_age> 2
The maximum size of stored chunks. When the storage grows beyond this size, the oldest chunks will be deleted.
Default: 10G
Choose a number from below, or type in your own value
1 / 500 MB
\ "500M"
2 / 1 GB
\ "1G"
3 / 10 GB
\ "10G"
chunk_total_size> 3
Remote config
--------------------
[test-cache]
remote = local:/test
plex_url = http://127.0.0.1:32400
plex_username = dummyusername
plex_password = *** ENCRYPTED ***
chunk_size = 5M
info_age = 48h
chunk_total_size = 10G
You can then use it like this,
List directories in top level of your drive
rclone lsd test-cache:
List all the files in your drive
rclone ls test-cache:
To start a cached mount
rclone mount --allow-other test-cache: /var/tmp/test-cache
Write Support
Writes are supported through cache.
One caveat is that a mounted cache remote does not add any retry or fallback
mechanism to the upload operation. This will depend on the implementation
of the wrapped remote.
One special case is covered with cache-writes which will cache the file
data at the same time as the upload when it is enabled making it available
from the cache store immediately once the upload is finished.
Read Features
Multiple connections
To counter the high latency between a local PC where rclone is running and cloud providers, the cache remote can split multiple requests to the cloud provider for smaller file chunks and combines them together locally where they can be available almost immediately before the reader usually needs them.
This is similar to buffering when media files are played online. Rclone will stay around the current marker but always try its best to stay ahead and prepare the data before.
Plex Integration
There is a direct integration with Plex which allows cache to detect during reading if the file is in playback or not. This helps cache to adapt how it queries the cloud provider depending on what is needed for.
Scans will have a minimum amount of workers (1) while in a confirmed playback cache will deploy the configured number of workers.
This integration opens the doorway to additional performance improvements which will be explored in the near future.
Note: If Plex options are not configured, cache will function with its
configured options without adapting any of its settings.
How to enable? Run rclone config and add all the Plex options (endpoint, username
and password) in your remote and it will be automatically enabled.
Affected settings:
cache-workers: Configured value during confirmed playback or 1 all the other times
Known issues
Windows support - Experimental
There are a couple of issues with Windows mount functionality that still require some investigations.
It should be considered as experimental thus far as fixes come in for this OS.
Most of the issues seem to be related to the difference between filesystems on Linux flavors and Windows as cache is heavily dependant on them.
Any reports or feedback on how cache behaves on this OS is greatly appreciated.
- https://github.com/ncw/rclone/issues/1935
- https://github.com/ncw/rclone/issues/1907
- https://github.com/ncw/rclone/issues/1834
Risk of throttling
Future iterations of the cache backend will make use of the pooling functionality of the cloud provider to synchronize and at the same time make writing through it more tolerant to failures.
There are a couple of enhancements in track to add these but in the meantime there is a valid concern that the expiring cache listings can lead to cloud provider throttles or bans due to repeated queries on it for very large mounts.
Some recommendations:
- don't use a very small interval for entry informations (
--cache-info-age) - while writes aren't yet optimised, you can still write through
cachewhich gives you the advantage of adding the file in the cache at the same time if configured to do so.
Future enhancements:
cache and crypt
One common scenario is to keep your data encrypted in the cloud provider
using the crypt remote. crypt uses a similar technique to wrap around
an existing remote and handles this translation in a seamless way.
There is an issue with wrapping the remotes in this order: cloud remote -> crypt -> cache
During testing, I experienced a lot of bans with the remotes in this order. I suspect it might be related to how crypt opens files on the cloud provider which makes it think we're downloading the full file instead of small chunks. Organizing the remotes in this order yelds better results: cloud remote -> cache -> crypt
Specific options
Here are the command line options specific to this cloud storage system.
--cache-chunk-path=PATH
Path to where partial file data (chunks) is stored locally. The remote name is appended to the final path.
This config follows the --cache-db-path. If you specify a custom
location for --cache-db-path and don't specify one for --cache-chunk-path
then --cache-chunk-path will use the same path as --cache-db-path.
Default: /cache-backend/ Example: /.cache/cache-backend/test-cache
--cache-db-path=PATH
Path to where the file structure metadata (DB) is stored locally. The remote name is used as the DB file name.
Default: /cache-backend/ Example: /.cache/cache-backend/test-cache
--cache-db-purge
Flag to clear all the cached data for this remote before.
Default: not set
--cache-chunk-size=SIZE
The size of a chunk (partial file data). Use lower numbers for slower connections.
Default: 5M
--cache-total-chunk-size=SIZE
The total size that the chunks can take up on the local disk. If cache
exceeds this value then it will start to the delete the oldest chunks until
it goes under this value.
Default: 10G
--cache-chunk-clean-interval=DURATION
How often should cache perform cleanups of the chunk storage. The default value
should be ok for most people. If you find that cache goes over cache-total-chunk-size
too often then try to lower this value to force it to perform cleanups more often.
Default: 1m
--cache-info-age=DURATION
How long to keep file structure information (directory listings, file size, mod times etc) locally.
If all write operations are done through cache then you can safely make
this value very large as the cache store will also be updated in real time.
Default: 6h
--cache-read-retries=RETRIES
How many times to retry a read from a cache storage.
Since reading from a cache stream is independent from downloading file data,
readers can get to a point where there's no more data in the cache.
Most of the times this can indicate a connectivity issue if cache isn't
able to provide file data anymore.
For really slow connections, increase this to a point where the stream is able to provide data but your experience will be very stuttering.
Default: 10
--cache-workers=WORKERS
How many workers should run in parallel to download chunks.
Higher values will mean more parallel processing (better CPU needed) and more concurrent requests on the cloud provider. This impacts several aspects like the cloud provider API limits, more stress on the hardware that rclone runs on but it also means that streams will be more fluid and data will be available much more faster to readers.
Note: If the optional Plex integration is enabled then this setting will adapt to the type of reading performed and the value specified here will be used as a maximum number of workers to use. Default: 4
--cache-chunk-no-memory
By default, cache will keep file data during streaming in RAM as well
to provide it to readers as fast as possible.
This transient data is evicted as soon as it is read and the number of
chunks stored doesn't exceed the number of workers. However, depending
on other settings like cache-chunk-size and cache-workers this footprint
can increase if there are parallel streams too (multiple files being read
at the same time).
If the hardware permits it, use this feature to provide an overall better performance during streaming but it can also be disabled if RAM is not available on the local machine.
Default: not set
--cache-rps=NUMBER
This setting places a hard limit on the number of requests per second that cache
will be doing to the cloud provider remote and try to respect that value
by setting waits between reads.
If you find that you're getting banned or limited on the cloud provider through cache and know that a smaller number of requests per second will allow you to work with it then you can use this setting for that.
A good balance of all the other settings should make this setting useless but it is available to set for more special cases.
NOTE: This will limit the number of requests during streams but other API calls to the cloud provider like directory listings will still pass.
Default: disabled
--cache-writes
If you need to read files immediately after you upload them through cache
you can enable this flag to have their data stored in the cache store at the
same time during upload.
Default: not set