This question is better asked on btrfs list. On 21.05.2022 22:35, Joe Salmeri wrote: ...
When I initially installed my TW system btrfs created the filesystem on a single SSD as follows:
data single metadata single system single
If I now use mkfs.btrfs on a new single SSD the btrfs filesystem is created as follows:
data single metadata DUP system DUP
In the man page the one statement that caught my attention was
"The deduplication in SSDs is thought to be widely available so the reason behind the mkfs default is to not give a false‚ sense of redundancy."
It seems like that man page information was written to explain why it originally created data/metadata/system all as single on a single SSD file system and was not updated to reflect that it is now using DUP for metadata and system.
So what is the recommendation now, should we convert single SSD installs to use DUP for metadata and system and then do I assume run balance or should we leave them as single?
It is up to you really. commit 65181c273e67bd48d01fc79f00826dce38b93c4c Author: David Sterba <dsterba@suse.com> Date: Tue Sep 28 00:29:53 2021 +0200 btrfs-progs: mkfs: don't autoselect DUP on SSD for metadata anymore The original idea of not doing DUP on SSD was that the duplicate blocks get deduplicated again by the driver firmware. This was in 2013, years ago. Then it was speculative and even nowadays we don't have much reliable information from vendors what optimizations are done on the drive level. After the year there's enough information gathered by user community and there's no simple answer. Expensive drives are more reliable but less common, for cheap consumer drive it's vice versa. The characteristics are described in more detail in manual page btrfs(5) in section "SOLID STATE DRIVES (SSD)". The reasoning is based on numerous reports on IRC and technical difficulty on mkfs side to do the right decision. The default is chosen to be the safe option and up to user to change that based on informed decision.