Austin S. Hemmelgarn posted on Thu, 03 Aug 2017 15:03:53 -0400 as excerpted:
>> Same thing with the trim feature that is marked OK . It clearly says >> that is has performance implications. It is marked OK so one would >> expect it to not cause the filesystem to fail, but if the performance >> becomes so slow that the filesystem gets practically unusable it is of >> course not "OK". The relevant information is missing for people to make >> a decent choice and I certainly don't know how serious these >> performance implications are, if they are at all relevant... > The performance implications bit shouldn't be listed, that's a given for > any filesystem with discard (TRIM is the ATA and eMMC command, UNMAP is > the SCSI one, and ERASE is the name on SD cards, discard is the generic > kernel term) support. The issue arises from devices that don't have > support for queuing such commands, which is quite rare for SSD's these > days. Not so entirely rare. The generally well regarded Samsung EVO/Pro 850 ssd series don't support queued-trim, and indeed, due to a fiasco where new firmware lied about such support[1], the kernel now blacklists queued- trim on all samsung ssds. (I actually bought a pair of samsung evo 1TB ssds after seeing them well recommended both on this list and in various reviews. Only AFTER I had them and was wondering if I could now add discard to my btrfs mount options and therefore googling for samsung evo queued trim specifically, did I find out about this fiasco and samsung not supporting linux because anyone can write the code, or I'd have certainly reconsidered and would have very likely spent my money elsewhere. I did actually check the current kernel's blacklisting code and verified it, tho I also noted it whitelists samsung ssds for actually honoring flush directives where the code treats non-whitelisted ssds as not honoring them due apparently to too many claiming to do so while not actually doing so, to get better performance, so it's a mixed bag, one whitelisting for actually flushing when it claims to, one blacklisting for not reliably handling queued-trim despite some firmware claiming to do so. But the worst IMO is samsung support blackballing linux because anyone can write the code. =:^ That's worth blackballing samsung for, in my book; I just wish I'd found out before the purchase instead of after, tho the linux devs have at least made sure samsung ssd users don't lose data on linux due to samsung's lies, despite samsung's horrible support policy blackballing linux, at least at the time.) --- [1] The firmware said it supported a new ata standard where it's apparently mandatory, but the result was repeatedly corrupted data, with samsung support repeatedly said they don't support Linux because anyone can write code to execute, but they weren't seeing the problem on MS yet simply because MS hadn't issued a release that supported the new standard, and had queued-trim disabled by default with the older standards due to such problems when it was enabled. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
