ZPOOL: Add a mirror to a concat zpool -

ZPOOL: Add a mirror to a concat zpool

# Tested on RHEL 6 & 7

# Even if ZFS can use individual slices or partitions, it is recommended to use whole disks.

# Having a concat zpool like following one

POOLNAME=my_pool

zpool status $POOLNAME
     pool: my_pool
    state: ONLINE
    scan: none requested
   config:

           NAME        STATE     READ WRITE CKSUM
           my_pool     ONLINE       0     0     0
             sdb       ONLINE       0     0     0
             sdc       ONLINE       0     0     0

   errors: No known data errors

zpool list
   NAME      SIZE ALLOC   FREE    CAP DEDUP HEALTH ALTROOT
   my_pool 19.9G   104K 19.9G     0% 1.00x ONLINE -

# we would like to add a mirror

DEVICE01_ORIG=/dev/sdb
DEVICE02_ORIG=/dev/sdc

DEVICE01_MIRR=/dev/sdd
DEVICE02_MIRR=/dev/sde

# We add one by one the new devices to the existing ones to form the new mirrors

zpool attach $POOLNAME $DEVICE01_ORIG $DEVICE01_MIRR

# If you have an error like this one:

   invalid vdev specification
   use '-f' to override the following errors:
   /dev/sdd does not contain an EFI label but it may contain partition
   information in the MBR.

# you should use '-f' option to create the pool - first ensure that disk(s) are the
# right one(s):

# zpool attach -f $POOLNAME $DEVICE01_ORIG $DEVICE01_MIRR

# Check

zpool status $POOLNAME
     pool: my_pool
    state: ONLINE
    scan: resilvered 36.5K in 0h0m with 0 errors on Tue Sep 1 15:18:06 2015
   config:

           NAME        STATE     READ WRITE CKSUM
           my_pool     ONLINE       0     0     0
             mirror-0 ONLINE       0     0     0
               sdb     ONLINE       0     0     0
               sdd     ONLINE       0     0     0   <----
             sdc       ONLINE       0     0     0

   errors: No known data errors

zpool attach $POOLNAME $DEVICE02_ORIG $DEVICE02_MIRR

# If you have an error like this one:

   invalid vdev specification
   use '-f' to override the following errors:
   /dev/sde does not contain an EFI label but it may contain partition
   information in the MBR.

# you should use '-f' option to create the pool - first ensure that disk(s) are the
# right one(s):

# zpool attach -f $POOLNAME $DEVICE02_ORIG $DEVICE02_MIRR

# Check

zpool status $POOLNAME
     pool: my_pool
    state: ONLINE
    scan: resilvered 64K in 0h0m with 0 errors on Tue Sep 1 15:18:45 2015
   config:

           NAME        STATE     READ WRITE CKSUM
           my_pool     ONLINE       0     0     0
             mirror-0 ONLINE       0     0     0
               sdb     ONLINE       0     0     0
               sdd     ONLINE       0     0     0   <----
             mirror-1 ONLINE       0     0     0
               sdc     ONLINE       0     0     0
               sde     ONLINE       0     0     0   <----

   errors: No known data errors

zpool list
   NAME      SIZE ALLOC   FREE    CAP DEDUP HEALTH ALTROOT
   my_pool 19.9G   116K 19.9G     0% 1.00x ONLINE -

# ------------------------------------------------------------------------------------------
# Adding a mirror to a concat zpool using disks of different sizes
# ------------------------------------------------------------------------------------------

# I will use two asymmetric disk partitions with the aim of giving an example:

lvmdiskscan | egrep "sdb1|sdc1"
     /dev/sdb1           [       5.00 GiB]
     /dev/sdc1           [      10.00 GiB]

# 1.- If we try to mirror a pool using a disk that is smaller than the existing one, this
# is what happens:

zpool create my_pool sdc1

zpool list my_pool
   NAME      SIZE ALLOC   FREE    CAP DEDUP HEALTH ALTROOT
   my_pool 9.94G 77.5K 9.94G     0% 1.00x ONLINE -

zpool attach my_pool sdc1 sdb1
   cannot attach sdb1 to sdc1: device is too small

# No problem so far: System prevents us from creating a mirror in a wrong way; that's all

# 2.- When adding a mirror using a disk that is larger than the existing one, we have to
# use the "autoexpand" property, that must be enabled for the whole size of the new disk
# to be used instead of limiting the pool to the original size. This will happens once
# the original disk has been removed from the pool, otherwise we would have an "asymmetric"
# mirror.

# Create a simple pool

zpool create my_pool sdb1

zpool list my_pool
   NAME      SIZE ALLOC   FREE    CAP DEDUP HEALTH ALTROOT
   my_pool 4.97G   109K 4.97G     0% 1.00x ONLINE -

# Enable "autoexpand"

zpool set autoexpand=on my_pool

# Add the mirror (new disk bigger than existing one)

zpool attach my_pool sdb1 sdc1

# Size remains constant...

zpool list my_pool
   NAME      SIZE ALLOC   FREE    CAP DEDUP HEALTH ALTROOT
   my_pool 4.97G   159K 4.97G     0% 1.00x ONLINE -

# ... until I detach the original disk. At that moment the pool is "autoexpanded"

zpool detach my_pool sdb1

zpool list my_pool
   NAME      SIZE ALLOC   FREE    CAP DEDUP HEALTH ALTROOT
   my_pool 9.97G   168K 9.97G     0% 1.00x ONLINE -

# If we had forgotten to enable auto-expansion before detaching the original disk, pool's
# size is not expanded even if we change "autoexpand" property afterwards. To get to
# expand the pool we have to run a "zpool online" command on the new disk(s)

zpool create my_pool sdb1

zpool attach -f my_pool sdb1 sdc1

zpool list my_pool
   NAME      SIZE ALLOC   FREE    CAP DEDUP HEALTH ALTROOT
   my_pool 4.97G   156K 4.97G     0% 1.00x ONLINE -

zpool detach my_pool sdb1

zpool list my_pool
   NAME      SIZE ALLOC   FREE    CAP DEDUP HEALTH ALTROOT
   my_pool 4.97G   156K 4.97G     0% 1.00x ONLINE -

# Ooops, I forgot to enable the autoexpand property, I will do it now...

zpool get autoexpand my_pool
   NAME     PROPERTY    VALUE   SOURCE
   my_pool autoexpand off     default

zpool set autoexpand=on my_pool

# No way, it doesn't work:

zpool list my_pool
   NAME      SIZE ALLOC   FREE    CAP DEDUP HEALTH ALTROOT
   my_pool 4.97G   172K 4.97G     0% 1.00x ONLINE -

# No problem, let's run an "online" on the new disk (even if it is already online)

zpool online my_pool sdc1

# and voilà!, the pool has been expanded:

zpool list my_pool
   NAME      SIZE ALLOC   FREE    CAP DEDUP HEALTH ALTROOT
   my_pool 9.97G   153K 9.97G     0% 1.00x ONLINE -