I have a SAN system with 10 drive slots setup with Software RAID10, and all the md0-5 added into a single volume group. The SATA port in slot 10 recently failed and will not accept any drive we put in there. I'm extremely nervous about leaving drive 9 unmirrored. My proposed solution is to add a USB external drive (matching size and manufacturer to drive #9) to the server and assign that as the RAID1 partner for #9. I realize that USB is going to be much slower than SATA, but I am more concerned about data protection than drive speed. 

Does anyone see any issues with that plan (other than performance)? 

cat /proc/mdstat
Personalities : [raid1] 
md4 : active raid1 sdj1[1]
 976759936 blocks [2/1] [U\_]

md3 : active raid1 sdc1[1] sda1[0]
 976759936 blocks [2/2] [UU]

md2 : active raid1 sdh1[1] sdg1[0]
 976759936 blocks [2/2] [UU]

md4 : active raid1 sdi1[0] sde1[1]
 976759936 blocks [2/2] [UU]

md0 : active raid1 sdf1[0] sdb1[1]
 976759936 blocks [2/2] [UU]