I went from LTO2 (IBM) to LTO4 (HP). My gut feeling is the IBM drives got somewhat higher compression. I no longer have any LTO2 stats but here is some observations from my current LTO4 tapes. I have just over 200 tapes. All backups are to staging then (de)staged to tape. I have two retentions – two weeks for incrementals and 6 weeks for fulls. All used tapes are removed each weekday and taken “offsite” – some are not full. Quite a few of the backups are multi-terabyte. I know from watching iostat that some sections of some servers compress well and some do not compress (in one case I have several terabytes of jpg’s).
Sorting Media and Device Management/Media/Volume Pools/NetBackup by “Kilobytes” I see on the high end 40 Full tapes with 1.1TB to 1.8TB but 2 tape are listed as Active with 1.6TB and 1.5TB. On the low end there are 21 Full tapes with .45TB to .64TB (this of course seems odd as LTO4 should contain at least 800GB).
Have seem tapes with just over 3TB but not today.
Anyone know if a tape is passed over because only large images remain to destage is set to “Full”? I have not observed this but with so many tapes marked Full with less than 600GB seems fishy to me.
Hope this helps,
GlenG