On Fri, 2015-06-26 at 11:43 +0200, Stefan Richter wrote: > On Jun 22 James Bottomley wrote: > > On Mon, 2015-06-22 at 13:30 -0400, Alan Stern wrote: > > > On Mon, 22 Jun 2015, James Bottomley wrote: > > > > Obviously, for a disk with a writeback cache that can't do flush, that > > > > window is much wider and the real solution should be to try to switch > > > > the cache to write through. > > > > > > I agree. Doing the switch manually (by writing to the "cache_type" > > > attribute file) works, but it's a nuisance to do this when you have a > > > portable USB drive that gets moved among a bunch of machines. > > > > Perhaps it might be wise to do this to every USB device ... for external > > devices, the small performance gain doesn't really make up for the > > potential data loss. > > Just a small note on the assumption of externally (and in extension, > temporarily) attached devices: Not all USB-attached devices are external, > and not all external devices are used as removable devices. The problems don't depend on the connection type: internal devices which have a writeback cache and don't accept flush commands have data integrity problems too. I can't really think of many situations where you'd be willing to sacrifice data integrity for performance. James > (For example, I am using 2 internal CD-ROMs via USB-2 + usb-storage and 2 > internal HDDs via USB 3 + uas in a PC with too few SATA ports and no PCIe > slot to spare for a controller add-on card, but plenty of USB headers > available on the mainboard. Similarly, some NASes have their operating > system located on a USB-attached device. Small offices use USB-attached > disks for backup and won't detach such a disk until rotation for off-site > deposit. Not to mention embedded computers with USB-attached but fixed > disks.) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
