XNAND2 Feature

XNAND2 is an innovation built upon its XNAND predecessor. This engineering effort was predicated by the NAND industry's falling quality standards and Technologic Systems' dedication to continued superior quality, long lifespan products. XNAND2 introduces a more robust system of redundant, error-corrected data storage, and a whole-device wear leveling system that ensures the longest possible lifespan for NAND media.

Please see our whitepaper on the subject for more detail and information.

To facilitate this new paradigm, a new 'nandctl' binary has been introduced. The features and output of this new utility are detailed in this section.

The command line options for the XNAND2 nandctl are very similar to the original:

# nandctl --help
Usage: nandctl [OPTION] ...
Technologic Systems NAND flash manipulation.

General options:
  -R, --read=N            Read N blocks of flash to stdout
  -W, --write=N           Write N blocks to flash
  -x, --writeset=BYTE     Write BYTE as value (default 0)
  -i, --writeimg=FILE     Use FILE as file to write to NAND
  -t, --writetest         Run write speed test
  -r, --readtest          Run read speed test
  -n, --random=SEED       Do random seeks for tests
  -z, --blocksize=SZ      Use SZ bytes each read/write call
  -k, --seek=SECTOR       Seek to 512b sector number SECTOR
  -d, --nbdserver=NBDSPEC Run NBD userspace block driver server
  -I, --bind=IPADDR       Bind NBD server to IPADDR
  -Q, --stats             Print NBD server stats
  -m, --dmesg             Print log of NAND activity
  -f, --foreground        Run NBD server in foreground
  -X, --xnand             Use XNAND RAID layer
  -I, --xnandinit         Initialize flash chip for XNAND
  -L, --listbb            List all factory bad blocks
  -v, --verbose           Be verbose (-vv for maximum)
  -P, --printmbr          Print MBR and partition table
  -M, --setmbr            Write MBR from environment variables
  -h, --help              This help

When running a NBD server, NBDSPEC is a comma separated list of
devices and partitions for the NBD servers starting at port 7525.
e.g. "lun0:part1,lun1:disc" corresponds to 2 NBD servers, one at port
7525 serving the first partition of chip #0, and the other at TCP
port 7526 serving the whole disc device of chip #1.

The --dmesg command will show a running event log since boot. This is useful for troubleshooting if a failure is suspected.

The --stats command will show a mixture of long-term and short-term statistical data about the NAND chip and the XNAND2 layer over it:

# nandctl --stats
nbdpid=146
nbd_readreqs=0
nbd_read_blks=0
nbd_writereqs=0
nbd_write_blks=0
nbd_seek_past_eof_errs=0
xnand2_most_worn=5936
xnand2_spares_used=6
xnand2_spares_remaining=1014
xnand2_total_erases=24156537
xnand2_ecc_fixups=0
xnand2_parity_recovers=0
read_seeks=0
write_seeks=0

This --stats output is helpful for systems where monitoring long-term health is useful.

Stats output definitions:
nbdpid: This is the process id of the nandctl process.
nbd_readreqs: This is the number of read requests received by nandctl since boot.
nbd_read_blks: This is the number of blocks read by the nbd client since boot.
nbd_writereqs: This is the number of write requests received by nandctl since boot.
nbd_write_blks: This is the number of blocks written by the nbd client since boot.
nbd_seek_past_eof_errs: This statistic should always read zero. It's the number of times the OS has asked nandctl to seek past the end of the media.
xnand2_most_worn: This is the number of writes that have been made to the most worn block on the NAND chip over the lifetime of the XNAND2 media.
xnand2_spares_used: This is the number of bad blocks marked by XNAND2 over the lifetime of the XNAND2 media.
xnand2_spares_remaining: This is the number of blocks not currently in active use by the disk block device or the RAID5 like redundant data backup.  They are available to participate in wear-leveling activities (along with the blocks used by the disk block device and redundant data).
xnand2_total_erases: This is the number of erases over the lifetime of the XNAND2 media since boot.
xnand2_ecc_fixups: This is the total number of ecc correctable errors XNAND2 has corrected since boot.
xnand2_parity_recovers: This is the total number of blocks XNAND2 has had to recover from parity data.
read_seeks: This is the number of read seeks done since boot.
write_seeks: This is the number of write seeks done since boot.