On 11/30/18 11:21 PM, Juha-Matti Tilli wrote: > Hello, > > (I'm not on the list, please CC me if you want a reply. Sorry if this is a > repost, I think my first message didn't get through as it was multipart and not > plain text.) > > The Samsung MZ7KM series devices that support ZERO after TRIM do not support > TRIM in RAID4/5/6 even if the special module parameter is enabled. The reason > is that the device name includes SAMSUNG but it does not include SSD even > though these server-grade storage devices are actually SSDs. The whitelist > contains only Samsung*SSD* and SAMSUNG*SSD*. The whitelist should contain > SAMSUNG*MZ7KM* as well. An alternative would be SAMSUNG* but then that would > match HDDs as well. Not sure if this has negative effects; in my current patch, > I only whitelist the MZ7KM devices. > > We tested with RAID1 that these SSDs genuinely read zero after TRIM by writing > a large file with random data, observing the data is present on the physical > disks, removing the file and running fstrim, and observing the data is now zero > on the physical disks. The device reports to read zero after TRIM to the > operating system, as well, but the operating system doesn't believe the device. > Because of our tests, I think the device should be believed to report the flag > correctly. For RAID1, the reads zero after TRIM flag is not needed, but > unfortunately, we have too much data to economically store it in RAID-1 with > three disks per mirror, and two disks per mirror would be too dangerous because > two failures could disable the array. > > As far as I know, this problem affects all versions of the Linux kernel. > Currently we have to run a custom manually compiled kernel with the patch, > because our use case is severely affected by lack of TRIM support (lots of data > stored, lots of I/O, nearly full disks, less than megabyte average file size, 1 > DWPD order of magnitude, uneconomical to use RAID-1 on the storage server). > > I reported this to Red Hat Bugzilla, but they wanted me to report this first to > this list, before the patch can be applied to Red Hat. > > Patch is here, sorry I use Gmail so I can't send the patch as a separate > git-send-email message given my current mail system: This patch is broken, can't be applied as-is. gmail works just fine with git send-email, that's what I use. My .gitconfig has this section: [sendemail] from = Jens Axboe <axboe@xxxxxxxxx> smtpserver = smtp.gmail.com smtpuser = axboe@xxxxxxxxx smtpencryption = tls smtppass = XXXXXXXXXXXXXXXXXX smtpserverport = 587 -- Jens Axboe
