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? > > Cheers, > Jes > > > Jes Sorensen (1): > raid0: Disable discard per default due to performance uncertainty > > drivers/md/raid0.c | 20 ++++++++++++++++++++ > 1 file changed, 20 insertions(+) > RAID1? RAID0?? I hate it when I do that! Doesn't the scheduler merge adjacent discard requests? Or is this some non-SATA/SCSI SSD that has a 'make_request_fn' driver? I think I came across one of those before (NVMe). In that case - the driver needs to be fixed. NeilBrown -- 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
