Optical media durability

At last I started clearing out the garage laundry room cupboards, which is where amongst much other stuff the optical media backups I take every week have been accumulating for many years. They have been stored in a fairly warm shirt-sleeve environment with no special precautions. So to get some idea of the durability of writable optical media, I've been somewhat randomly pulling groups of backups out of the stacks and re-verifying the MD5 checksums, which were all verified immediately after writing.

TL;DR: Surprisingly, I'm getting good data from CD-Rs more than 14 years old, and from DVD-Rs nearly 12 years old. Your mileage may vary. Below the fold, my results.

Month	Media	Good	Bad	Vendor
01/04	CD-R	5	0	GQ
05/04	CD-R	5	0	Memorex
02/06	CD-R	5	0	GQ
11/06	DVD-R	5	0	GQ
12/06	DVD-R	1	0	GQ
01/07	DVD-R	4	0	GQ
04/07	DVD-R	3	0	GQ
05/07	DVD-R	2	0	GQ
07/11	DVD-R	4	0	Verbatim
08/11	DVD-R	1	0	Verbatim
04/13	DVD+R	2	0	Optimum
05/13	DVD+R	3	0	Optimum

The fields in the table are as follows:

• Month: The date marked on the media in Sharpie, and verified via the on-disk metadata.
• Media: The type of media.
• Good: The number of media with this type and date for which all MD5 checksums were correctly verified.
• Bad: The number of media with this type and date for which any file failed MD5 verification.
• Vendor: the vendor name on the media

The media are generic, low-cost CD-R and DVD-+R media purchased in 50s and 100s from Fry's in Palo Alto. Several of the CD-Rs caused errors like this during the initial mount, but nevertheless succeeded in verifying their MD5s:

sr 6:0:0:0: [sr0] tag#0 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE
sr 6:0:0:0: [sr0] tag#0 Sense Key : Medium Error [current]
sr 6:0:0:0: [sr0] tag#0 Add. Sense: L-EC uncorrectable error
sr 6:0:0:0: [sr0] tag#0 CDB: Read(10) 28 00 00 05 64 30 00 00 02 00 00 00
blk_update_request: critical medium error, dev sr0, sector 1413312
sr 6:0:0:0: [sr0] tag#0 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE
sr 6:0:0:0: [sr0] tag#0 Sense Key : Medium Error [current] 
sr 6:0:0:0: [sr0] tag#0 Add. Sense: L-EC uncorrectable error
sr 6:0:0:0: [sr0] tag#0 CDB: Read(10) 28 00 00 05 64 30 00 00 02 00 00 00 
blk_update_request: critical medium error, dev sr0, sector 1413312
Aug 12 14:34:37 nuc7 kernel: [194688.719850] Buffer I/O error on dev sr0,
                             logical block 176664, async page read

I never intended these weekly backups to be a long-term archive. The intended use was disaster recovery; until now I was just too lazy to dispose of the back catalog. I've retained the sample of disks for future re-analysis.  But the remaining approximately 1200 older than 3 years will be recycled by the CD Recycling Center of America, once I figure out how to ship 45lbs of optical disks!

I'm sorry that the sample isn't bigger, but it was time-consuming feeding 40 disks into the reader, and I need the space in the cupboards now.