smooth disk replacement and expansion from 8 to 14Tb

I passed from 8Tb to 14Tb easily in 10 steps

initial config

1 raid array Raid 1 4TB a

1 raid array Raid 1 2TB b

1 raid array Raid 1 2TB c

final config

1 raid array Raid 1 6TB a

1 raid array Raid 1 4TB b

1 raid array Raid 1 4TB c

purchased 2 x 6Tb + 2 x 4Tb

1 b 2TB exchanged with 4Tb disk 1 (5hrs to rebuild array from degraded to redundant)

2 c 2TB exchanged with 4Tb disk 1 (5hrs to rebuild array from degraded to redundant)

3 a 4TB exchanged with 6Tb disk 1 (7hrs to rebuild array from degraded to redundant)

4 a 4TB exchanged with 6Tb disk 2 (7hrs to rebuild array from degraded to redundant then 6hrs to 6Tb array capacity)

5 a low level reformat 4Tb disk 1 3hrs

6 a low level reformat 4Tb disk 2 3hrs

7 b 2TB exchanged with 4Tb disk 2 (5hrs to rebuild array from degraded to redundant then 5hrs to 4Tb array capacity)

8 c 2TB exchanged with 4Tb disk 2 (5hrs to rebuild array from degraded to redundant then 5hrs to 4Tb array capacity)