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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-05 11:19:16 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-05 12:07:37 +0000
commitb485aab7e71c1625cfc27e0f92c9509f42378458 (patch)
treeae9abe108601079d1679194de237c9a435ae5b55 /health/guides/disks/bcache_cache_errors.md
parentAdding upstream version 1.44.3. (diff)
downloadnetdata-b485aab7e71c1625cfc27e0f92c9509f42378458.tar.xz
netdata-b485aab7e71c1625cfc27e0f92c9509f42378458.zip
Adding upstream version 1.45.3+dfsg.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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-### Understand the alert
-
-This alert is triggered when the number of read races in the last minute on a `bcache` system has increased. A read race occurs when a `bucket` is reused and invalidated while it's being read from the cache. In this situation, the data is reread from the slower backing device.
-
-### What is bcache?
-
-`bcache` is a cache within the block layer of the Linux kernel. It enables fast storage devices, such as SSDs (Solid State Drives), to act as a cache for slower storage devices like HDDs (Hard Disk Drives). This creates hybrid volumes with improved performance. A cache device is usually divided into `buckets` that match the physical disk's erase blocks.
-
-### Troubleshoot the alert
-
-1. Verify the current `bcache` cache errors:
-
- ```
- grep bcache_cache_errors /sys/fs/bcache/*/stats_total/*
- ```
-
- This command will show the total number of cache errors for all `bcache` devices.
-
-2. Identify the affected backing device:
-
- You can determine the affected backing device by checking the `/sys/fs/bcache` directory. Look for the symbolic link that points to the problematic device.
-
- ```
- ls -l /sys/fs/bcache
- ```
-
- This command will show the list of devices with corresponding names.
-
-3. Monitor the cache device's performance:
-
- Use `iostat` to check the cache device's I/O performance.
-
- ```
- iostat -x -h -p /dev/YOUR_CACHE_DEVICE
- ```
-
- Note that you should replace `YOUR_CACHE_DEVICE` with the actual cache device name.
-
-4. Check the utilization of the cache and backing devices:
-
- Use the following commands to check the utilization percentage of the cache and backing devices:
-
- ```
- # for the cache device (/dev/YOUR_CACHE_DEVICE)
- cat /sys/block/YOUR_CACHE_DEVICE/bcache/utilization
-
- # for the backing device (/dev/YOUR_BACKING_DEVICE)
- cat /sys/block/YOUR_BACKING_DEVICE/bcache/utilization
- ```
-
- Replace `YOUR_CACHE_DEVICE` and `YOUR_BACKING_DEVICE` with the respective device names.
-
-5. Optimize the cache:
-
- - If the cache utilization is high, consider increasing the cache size or adding more cache devices.
- - If the cache device is heavily utilized, consider upgrading it to a faster SSD.
- - In case the read races persist, consider using a [priority caching strategy](https://www.kernel.org/doc/html/latest/admin-guide/bcache.html#priority-caching).
-
- You may also need to review your system's overall I/O load and adjust your caching strategy accordingly.
-
-### Useful resources
-
-1. [Bcache: Caching beyond just RAM](https://lwn.net/Articles/394672/)
-2. [Kernel Documentation - Bcache](https://www.kernel.org/doc/html/latest/admin-guide/bcache.html)
-3. [Arch Linux Wiki - Bcache](https://wiki.archlinux.org/title/bcache)
-4. [Wikipedia - Bcache](https://en.wikipedia.org/wiki/Bcache)