Ever notice how many people have 60's with failing drives? Well, a large part of it comes from using HD disks. just because you didn't run into problems doesnt mean you wont in the future. Well, now that you have SCSI you probably never use the drive, but yes, HD disks use a diferent magnetic standard, it can mess up your drive because both the disk and the drive are magnetic, and so they mess with each other if miss matched. if I remember right, the DD drive can't write the data deep enough onto the disk, so you get a lot of failed disks and corrupted data over time, after a lot of HD disk use, your drive will lose its power to properly write and Format floppies. Then you get a lot of bum disks and a lot of disks not recognized.
DD disks are cheap, I bought 100 of them for $20 and almost finished them by the time I got my SCSI upgrade. You should use the disks the drive was designed to use. Unless you have a replacement drive that can handle both disks.
http://www.superwarehouse.com/Imation_3.5_DS_DD_Floppy_(10_pk)/12882/p/46719
http://search.ebay.com/DD-Disk_W0QQsofocusZbsQQsbrftogZ1QQfromZR10QQsacatZ-1QQcatrefZC6QQsargnZ-1QQsaslcZ2QQsadisZ200QQfposZ10708QQftrtZ1QQftrvZ1QQfsopZ1QQfsooZ1