What is a tape drive

A tape drive writes data along a long length of tape to which a magnetizable coating has been applied. The attraction is the the tape once written may be removed from the drive for backup or archival purposes.

The main snag with with tape cartridges is that too locate information the tape must be read from the beginning. This is very time consuming and ineficient if only a small amount of data is to be recovered.

Drive Comparison

The following table provides a brief comparison of a number of current and passed tape drive, for the IBM RS6000 range.

Where a drive supports a compression algorithum the corresponding performance, and capacity figures are included. This presupposes that the data to be backed up is readily compressible like text or HTML files.

If the data to be backed up is already compressed, {.jpg, .gif, .Z, .z, } the drives compression option will not provide any additional compression and may in some cases slow the backup down or reduce the capacity.

The following table is sorted by backup speed. Prices are idicative only, additional charges for cables, controlers, racks, etc may be applicable.

Past and present Tape Drives
 Model  Media  Performance  Capacity  Interface  Mounting  Guide
     Native  Compresed  Native  Compresed  type  style  Price
 7207-011  QIC(1/4-inch)  200KB/s  N/A  525MB  N/A  SCSI  Table Top  
 7207-012  QIC(1/4-inch)  300KB/s  N/A  1.2GB  N/A  SCSI  Table Top  
 7207-122  QIC(1/4-inch)  380KB/s  760KB/s  4GB  8GB  SCSI-2  Table Top  £1,160
 7206-005  4mm DDS-2 Data Cartridge  400KB/s  800KB/s  4GB  8GB  SCSI-2  Table Top  £1,739
 7208-011  8mm Data Cartridge  500KB/s  1MB/s  5GB  10GB  SCSI-2  Table Top  
 7206-110  4mm DDS-3 Data Cartridge  1.1MB/s  2.2MB/s  12GB  24GB  SCSI-2  Table Top  £1,904
 7207-315  QIC(1/4-inch)  1.5MB/s  3.0MB/s  13GB  26GB  SCSI-2  Table Top  £3,240
 3570-B00  Magstar MP Fast Access Linear Tape  2.2MB/s  6.6MB/s  5GB  15GB  SCSI-2 Differential  External  £5,611
 3490-E01  1/2-inch  3MB/s  6.8MB/s  0.8GB  2.4GB  SCSI-2  Table Top  
 3490-F01  1/2-inch  3MB/s  6.8MB/s  0.8GB  2.4GB  SCSI-2  Deskside  £15,778
 3490-F11  1/2-inch  3MB/s  6.8MB/s  0.8GB  2.4GB  SCSI-2  Rackmount in FC0 Rack  £15,778
 7208-341  8mm Data Cartridge  3MB/s  6MB/s  20GB  40GB  SCSI-2  Table Top  £3,900
 7205-311  1/2-inch DLT  5MB/s  10MB/s  35GB  70GB  SCSI-2 differential  Table Top  £7,577
 3570-C00  Magstar MP Fast Access Linear Tape  7.0MB/s  15.0MB/s  5GB  15GB  SCSI-2 Differential  External  £9,828
 3590-B11  1/2-inch  9MB/s  13MB/s  10GB  30GB  SCSI-2  Rack mount  £22,943
 3590-E11  1/2-inch  14MB/s  34MB/s  20GB  60GB  Ultra SCSI  Rack mount  £32,107

Tape Drive Performance

With regard to performance the figures given are for the tape drive with the data being supplied at an optimum block size. If the next block of data is not available to the drive when it is ready for it, the drive must stop and wait. Given that hard disks can have a sequential access rate of as little as 50KB/s.

It is vary easy to find especially with the faster tape drives that the tape drive is waiting for the disks, rather than the system waiting for the tape drive. With the faster drives the source files must be on a striped or mirrored LV to make use of the tape drives speed. If backup performance falls below half the expected speed, check vmstat or iostat while a file backup is running. If these show the system to be disk bound check for file fragmentation, other wise it may be worth trying a larger block size if possible.

Tape Drive Dencity settings

Some dives support multiple density setings. {the lsattr command lists attributes density_set_1, and density_set_2}

Density settings
 Density  Drive  Description
00 * Hardware default for drive
2 1/2 inch 9-Track Tape 1600 bpi
3 1/2 inch 9-Track Tape 6250 bpi
15 QIC DC600A/DC6000 60MB QIC-120 cartridge
16 QIC DC6150/MC6150 150MB QIC-150 cartridge
17 QIC DC6525/MC6525 525MB QIC-525 cartridge
19 4mm DDS3 drive 2GB DDSiii cartridge {2:1 compression posible}
20 8mm 5GB 2.3GB mode
21 QIC QIC1000 1GB cartridge
21 8mm 5GB 5GB mode no hardware compression
23 35GB 7205-311 DLTtapeIII cartridge 2.6GB no hardware compression
24 35GB 7205-311 DLTtapeIII cartridge 6GB no hardware compression
25 35GB 7205-311 DLTtapeIII cartridge 10GB {2:1 compression posible}
25 35GB 7205-311 DLTtapeIIIxt cartridge 15GB {2:1 compression posible}
26 35GB 7205-311 DLTtapeIV cartridge 20GB {2:1 compression posible}
27 35GB 7205-311 DLTtapeIV cartridge 35GB {2:1 compression posible}
33 QIC QIC-5010-DC 13GB cartridge
34 QIC QIC-2GB 2GB cartridge
36 4mm DDS3 drive 4GB DDS2 cartridge {2:1 compression posible}
37 4mm DDS3 drive 12GB DDS3 cartridge {2:1 compression posible}
39 8mm 20GB 20GB mode hardware compression if configured
140 8mm 5GB 5GB mode hardware compression if configured
15 QIC
15 QIC