On 11/29/2016 07:59 AM, Patrick Dung wrote: > Hello, > > Sorry if it is a cross posting. > I had post my question in linux-lvm mailing list but did not have reply. > > In my old setting, fstrim is supported: > ext4 over LVM over MD software raid 1 (mdadm) > SSD. > > After reading the recommendation in RHEL 6 > https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Storage_Administration_Guide/ch-ssd.html > > I changed to use raid 1 mirror using 'LVM RAID logical volume'. It > make use of MD raid internally. > But I found fstrim does not work anymore. Is the behavior expected? I can't remember when it was changed, but md raid is only trustworthy for the mirroring types, and only if the underlying devices return zeroes when reading trimmed blocks. Since this isn't guaranteed, and I recall reading that some devices that claim to return zeroes don't, md raid cannot determine automatically if it is safe. Theoretically, raid5 could be compatible if the underlying device returns zeros, and trims always cover entire stripes. But that would require code within mdadm to track stripe-fragment trims that have been received. Blegh. Phil -- 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
