Comment by blobdole
5 days ago
Beautiful.
Defragmenting my drives manually is one of those things like closing apps on my phone I am not using. Everyone says there is no need to do it. It might even be slightly worse overall. I even have enough self control to avoid doing it and have for years...
But deep down in my heart, I truly FEEL like if I did it would improve things... somehow.
I discovered that tested performance on copper-rs a high performance OS for robotics when I run it on ext4 and what is annoying in robotics is the max latency & jitter. Especially that we allocate large slabs in copper so this is not helping at all.
This is on a slow device but it might be worse on a fast one as the extra allocation of small extents start to hit harder on the host side:
(fragmented relative to baseline) bandwidth: 100.65 -> 94.74 MiB/s (-5.86%) elapsed time: 339.550 -> 360.699 s (+6.23%) mean latency: 9935.7 -> 10554.6 us (+6.23%) p50 latency: 6715.2 -> 6838.9 us (+1.84%) p95 latency: 19394.4 -> 20599.9 us (+6.22%) p99 latency: 131498.2 -> 131988.3 us (+0.37%) max latency: 183713.2 -> 624392.9 us (+239.87%) jitter stddev: 17823.1 -> 19806.0 us (+11.13%) jitter CV: 179.38 -> 187.65% (+4.61%)
Also check your nvme granularity with fstrim -D if you are on 4KB your nvme is so fine grain that it doesn't matter much but if it is 64KB like my main one. Ouch, those small files in the middle of the 64KB won't magically go away.
I feel so seen right now. My partner complains about me closing apps on my phone consistently. I also have to hold myself back from defragging and continually cleaning up my storage drives.
I too am nearly certain that the positive benefits are approaching nil, but I still feel it should be helpful.
> My partner complains about me closing apps on my phone consistently.
I'd be curious to know the reqson why she would care on her own phone and why it would be an issue on someone else's phone?
At least on iPhone, it basically doesn't do anything. Apple aggressively kills all background apps automatically. the "open" apps in the switcher are almost always just screenshots of previously-open-but-now-closed apps. if it was recent, the latest app or two in the switcher might actually be open, but rarely more than that.
Despite this, many of my relatives have somehow learned this habit of opening the switcher and closing all apps when they are done with them.
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> My partner complains about me closing apps on my phone consistently.
Which one of you is neurotic?
I know it’s a late reply, but the answer is absolutely both of us are exceptionally neurotic. But in completely different ways.
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When you die, you will leave behind nice orderly contiguous files. It's thoughtful. hehe
After digging through a recently passed relative’s hard drive (the computer barely functioned so I pulled it) and having to search through years of garbage that where never deleted to find the photos, Word documents, and WordPerfect documents my aunt ‘knew’ where stored there somewhere, this is not an insignificant gift to leave my family with.
only HDD drives I use are in a ZFS pool which has a very usable fragmentation value from zpool.
In case you (or others aren’t aware) the FRAG value ZFS shows, is an arbitrary calculation to help give a value to free space fragmentation.
The purpose is to have a sense of when ZFS may developing trouble quickly finding contiguous blocks of free space to dump new data into. Mostly only a concern for high active and highly full pools. When you start watching the number climb past double digits, you may start finding performance issues but it’s a very contextual thing, rather than “at x value it’s bad”.
Basically it has nothing to do with written file fragmentation, or potential read speed.
Because ZFS is a copy on write filsystem, attempts at defragmentation an active pool are generally not effective. An exception would be a pool that is full of large files that was written in a non contiguous way (like torrents), in which case copying the data to a new dataset and deleting the old roughly achieves the purpose. Or you could use something like https://github.com/salesforce/zfs_defrag
Wow! I did not know that, thank you for the info.
Indeed torrents were the most obvious cause of the fragmentation I saw.
Except for some backups, all of my machines use solid state storage so I don't think there is a point for most people, is there?
Sequential reads are faster for SSDs. As long as defragmentation is reducing the chance of doing a random read, it is beneficial.
OH! TIL! Apparently
Still, given SSDs have a lifespan and given few of my files are that large, I think I'm personally okay without defragmenting. Those numbers are impressive but, most of 10s of thousands of files are source code text files. Asking online what the real-world loss is from not defragmenting
> You are giving up virtually 0% to 3% of real-world performance. In daily development, media editing, and standard system use, defragmenting your SSD will yield no human-noticeable speedup.
Is it possible to determine which sectors are physically sequential given remapping for wear-leveling?
Otherwise the claimed defragmentation here is not actually resulting in sequential data.
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Prefetching applies to SSDs too, and that's generally sequential in some sense.
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If it makes it feel faster, it makes it feel faster.
It's like those copper bangles with magnets that people swear makes their joints less creaky.
My example is a daith piercing, that's when you pierce a ring through a fold of cartilage in a certain spot inside your ear. It's supposed to stop you getting migraines, but there's no sensible mechanism for this to work. It's all woo and bunkum, apparently.
But I've had four migraines in eight years as opposed to four every month.
So, if it feels faster, it might well be.