Roman Mamedov <rm@xxxxxxxxxxx> writes: > On Tue, 23 Jun 2015 20:26:12 -0400 > Jes.Sorensen@xxxxxxxxxx wrote: > >> From: Jes Sorensen <Jes.Sorensen@xxxxxxxxxx> >> >> Neil, >> >> I have been hitting issues with discard being ridiculously slow on >> arrays with certain typs of SSDs that seem to serialize discard >> processing. >> >> This is particularly bad as I have seen systems where the IMSM BIOS >> defaults to 4KB chunk size, combined with these badly performing >> drives, it could bump the mkfs on an array from seconds to over 40 >> minutes. Most users will stick to the defaults and then hit the >> problem during install without understanding why it goes wrong :( >> >> The problem is that there is no way to benchmark our way to this or >> somehow test if a drive performs discard at reasonable speed. I >> suggest we take an approach similar to that of RAID456 and default to >> disabling discard, except for the case where the user knows the drives >> are safe. >> >> Thoughts? > > It's very unfortunate if you would cripple all the good SSD models because of > a few bad ones. No one will remember to explicitly put the override to enable > TRIM, or perhaps even know that it gets disabled in md in the first place. The > only thing they will later notice is lowered performance and lifespan of their > SSDs. We already disable discard per default on raid456 in a similar manner because some of them unreliably reports discard_zeroes_data when they in reality don't. If there was a way to reliably detect these things it would be fine, unfortunately there isn't. Jes -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
