On Fri, Feb 15, 2008 at 1:25 PM, Joseph L. Casale <[EMAIL PROTECTED]> wrote: > Exactly? They are 200/400 tapes.
I ignore "compressed capacity" claims; they are a marketing gimmick and always have been. Compression rates vary tremendously. You might get no compression gain, or 1.5:1, or 3:1. So I just avoid quoting "compressed capacity" entirely. By "200/400 tape", I surmise you LTO-2. Those do have a nominal, native capacity of 200 GB. But in the land of disks and tapes, "200 GB" means "200 billion bytes". In the land of software and operating systems, "200 GB" means "200 * 2^30 bytes". This is sometimes explicitly written as "200 GiB". Compare: 200 GB = 200,000,000,000 bytes 200 GiB = 214,748,364,800 bytes 14 GiB = 14,748,364,800 bytes (difference) So right away, you're only going to get 93% of that "200 GB" you thought you had. Then there is overhead for metadata. Is this a large number of small files? If so, the metadata for each file may be becoming significant. I don't know anything about BUE's on-tape format, but I would guess they are likely storing a header at the start of each file (with name, datestamps, size, NTFS ACL, etc.). Or maybe in a catalog at the start/end of the tape. Either way, it consumes tape space. You also loose some tape capacity to bad blocks. Any big tape is going to have some number of bad blocks. Nominally, the drive automatically detects and corrects for them, so the backup software (and you) are not aware it is even happening. But it can eat into the nominal capacity of the tape. Is it an old tape? Finally, yes, a bad or simplistic compression algorithm may well make the "compressed" data larger for already-compressed input. A smart compression implementation will detect this and just store the straight input data, but tape drives are not known for using smart implementations. So turning off hardware compression may well gain you some tape space back. But perhaps not as much as you think. -- Ben ~ Upgrade to Next Generation Antispam/Antivirus with Ninja! ~ ~ <http://www.sunbelt-software.com/SunbeltMessagingNinja.cfm> ~
