Slack on optical disk

Sergio_18 — Tue, 30 Apr 2002 10:15:16 GMT

When I transfer data files from hard disk to optical disk I have
a big slack, almost 2:1.
I have following system:
Windows 2000 Server;
NTFS drives 1.024 cluster size;
Jukebox: HP Surestore 1200mx, 128 slots.
Optical disk: HP C7984A 4096 bytes/sector, WORM, 9.1 GB, .
InveStore 3.43.
Data files:
One data volume of 1 GB has around 250.000 files.
I am able to put only around 2 GB on 4.5 GB side of optical
disk.

I will appreciate any help.

Re: Slack on optical disk

CA628575 — Tue, 30 Apr 2002 11:03:47 GMT

I'm not familiar with the Investor software, but I suspect the reason is that you have relatively large number of smaller files, and a pretty big sector size on the optical disk (4KB). Due to the WORM characteristics the filesystem / software cannot use fragmentation on the blocks to only use partial blocks.

The rule of thumb is that you will on average waste 1/2 block per file in capacity, as the last block of the file will rarely align with block boundaries.

Given your paramters, you should expect to waste 250,000 * 4KB * 1/2 = 500MB.

And then you need to account for the filesystem meta-data, which again due to the WORM characteristics can often not be stored as efficiently as on a disk-based filesystem. The worst case scenario here is that the software uses one one extra block per file - this would amount to another 250,000 * 4KB = 1GB.

I'm not sure about your solution, but you could look into combining smaller files into larger archive files before moving them to WORM. That would dramatically cut down on the wasted capacity.

topic Slack on optical disk in Optical Jukeboxes and Drives

Slack on optical disk

Re: Slack on optical disk