Most classic Macs use a hard disk drive as their main mass storage medium. Some of the latest 68k Macs and the majority of PPC Macs use IDE harddisk drives. The majority of 68k Macs uses SCSI hard disk drives of a kind not in production any more, but. An option to replace a defective SCSI harddisk drive is the use of a recent SATA harddisk drive in combination with a SCSI-SATA converter / bridge device (or a chain of a SATA-IDE bridge and an IDE-SCSI-bridge). This allows to use a SATA harddisk drive just like a common SCSI harddisk drive, with a jumper table to set SCSI ID number, termination, parity etc. Different makes are available. As modern SATA-SCSI bridges are made for recent server computers and RAIDs, an additional adapter will be necessary to fit the HD68 pin or VHDCI 68 pin connector used in Ultra LVD160 SCSI devices to the 50 pin IDC connector used in vintage SCSI drives.
In case you look for an alternative have a look at the following article in this wiki: SCSI harddisk replacement options.
Several products to support recent SCSI systems are available. Most of the products are intended for use in recent server arrangements, to provide a "low cost" alternative compared to recent high speed SCSI drives, which needs not to be a low cost solution in a hobbyists terms.
If you have recent information about additional devices or availability, update this page, please.