how to use USB hard disk as /(root)

[hatahata]

now
i give up to use hard disk as root , becasue of /boot/uEnv.txt in spite of your kind advice .
so use hard disk as swap , tmp and /SAVE( www files and /home/debian/SAVE folda lives in this folda by ln -s )

anyway

/etc/fstab
/dev/mmcblk0p1 /boot vfat defaults 0 2
/dev/mmcblk0p2 / ext4 defaults,noatime 0 1
/dev/sda1 /SAVE ext4    defaults,noatime                0               1    
/dev/sda2 none   swap    sw                             0               0
/dev/sda3 /tmp  ext4    defaults,noatime                0               1

$ df
ファイルシス   1K-ブロック    使用    使用可 使用% マウント位置
/dev/mmcblk0p2    29034620 3522568  24032892   13% /
devtmpfs            468608       0    468608    0% /dev
tmpfs               502140       0    502140    0% /dev/shm
tmpfs               502140    7032    495108    2% /run
tmpfs                 5120       4      5116    1% /run/lock
tmpfs               502140       0    502140    0% /sys/fs/cgroup
/dev/mmcblk0p1       51082   12188     38894   24% /boot
/dev/sda3         10190136   23040   9626424    1% /tmp
/dev/sda1        226815536 2157776 213113076    2% /SAVE
tmpfs               100432       4    100428    1% /run/user/117
tmpfs               100432       0    100432    0% /run/user/1000

top - 03:16:01 up 24 min,  2 users,  load average: 0.66, 0.45, 0.53
Tasks: 115 total,   1 running, 114 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.1 us,  0.1 sy,  0.0 ni, 97.8 id,  2.1 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem:   1004284 total,   984560 used,    19724 free,     6704 buffers
KiB Swap:  3145724 total,        0 used,  3145724 free.   822912 cached Mem

#chown -R debian /SAVE
$ cd /SAVE

Code:

$  sysbench --test=fileio --file-test-mode=seqwr run
sysbench 0.4.12:  multi-threaded system evaluation benchmark

Running the test with following options:
Number of threads: 1

Extra file open flags: 0
128 files, 16Mb each
2Gb total file size
Block size 16Kb
Periodic FSYNC enabled, calling fsync() each 100 requests.
Calling fsync() at the end of test, Enabled.
Using synchronous I/O mode
Doing sequential write (creation) test
Threads started!
Done.

Operations performed:  0 Read, 131072 Write, 128 Other = 131200 Total
Read 0b  Written 2Gb  Total transferred 2Gb  (14.557Mb/sec)
931.68 Requests/sec executed

Test execution summary:
  total time:                          140.6836s
  total number of events:              131072
  total time taken by event execution: 130.1792
  per-request statistics:
       min:                                  0.05ms
       avg:                                  0.99ms
       max:                               1223.67ms
       approx.  95 percentile:               9.55ms

Threads fairness:
  events (avg/stddev):           131072.0000/0.00
  execution time (avg/stddev):   130.1792/0.00



$ rm test*

when i run sysbench in other than hard disk , the result is
Threads fairness:
events (avg/stddev): 131072.0000/0.00
execution time (avg/stddev): 170.4893/0.00
in spite of using 'read up to 85 MB/s sd card)'


when i want to return it to the beginning(sd card only system ) , i only rewrite /etc/fstab originally .
easy
---
regards

my banana pi M1 has sata interface and sata hard disk and use sata hard disk as root .
(/dev/sda1 236235700 84716984 139518556 38% /)
in this case the result is next
Threads fairness:
events (avg/stddev): 131072.0000/0.00
execution time (avg/stddev): 56.8743/0.00 <---fast 2X