Linux software RAID5 on SSD. One SSD 40% more worn out than the others

We have a 6 SSD, RAID5 volume. The SSD disks we are using are Crucial M4-CT512M4SSD2 firmware 000F. We write 100 ~ 200GB data through MySQL InnoDB to the volume daily. The RAID5 volume is only used for MySQL and nothing else.

Output of lsscsi:

    [0:0:0:0]    disk    iDRAC    LCDRIVE          0323  /dev/sdb 
    [1:0:0:0]    cd/dvd  iDRAC    Virtual CD       0323  /dev/sr0 
    [1:0:0:1]    disk    iDRAC    Virtual Floppy   0323  /dev/sdc 
    [2:2:0:0]    disk    DELL     PERC H700        2.10  /dev/sda 
    [3:0:0:0]    disk    ATA      M4-CT512M4SSD2   000F  /dev/sdd 
    [3:0:1:0]    disk    ATA      M4-CT512M4SSD2   000F  /dev/sde 
    [3:0:2:0]    disk    ATA      M4-CT512M4SSD2   000F  /dev/sdf 
    [3:0:3:0]    disk    ATA      M4-CT512M4SSD2   000F  /dev/sdg 
    [3:0:4:0]    disk    ATA      M4-CT512M4SSD2   000F  /dev/sdh 
    [3:0:5:0]    disk    ATA      M4-CT512M4SSD2   000F  /dev/sdi 
    [3:0:6:0]    enclosu LSI CORP SAS2X36          0717  -       
    [3:0:7:0]    enclosu LSI CORP SAS2X36          0717  -       

Output of smartctl : (see here for attribute 173)

for p in d e f g h i ; do smartctl -A /dev/sd${p} | grep 173  ; done

173 Unknown_Attribute       0x0033   098   098   010    Pre-fail  Always       -       67
173 Unknown_Attribute       0x0033   098   098   010    Pre-fail  Always       -       66
173 Unknown_Attribute       0x0033   098   098   010    Pre-fail  Always       -       71
173 Unknown_Attribute       0x0033   098   098   010    Pre-fail  Always       -       66
173 Unknown_Attribute       0x0033   098   098   010    Pre-fail  Always       -       69
173 Unknown_Attribute       0x0033   097   097   010    Pre-fail  Always       -       105

And the output for /proc/mdstat:

Personalities : [raid6] [raid5] [raid4] 
md0 : active raid5 sdi[6] sdg[3] sdh[4] sdf[2] sdd[0] sde[1]
  2500532160 blocks super 1.2 level 5, 64k chunk, algorithm 2 [6/6] [UUUUUU]
  bitmap: 3/4 pages [12KB], 65536KB chunk

 unused devices: <none>

We are unsure why "sdi" is more than 40% more worn out than other disks, as the parity should be evenly distributed across all disks.

It's just rounding error. This is the smallest difference SMART is capable of showing. Likely over the next few days, the other SSDs will switch to 097 one by one.