The HARDWARE 2 training: servers, networks and communication

9. Backup and tapes dives in network

9.1. Introduction - 9.2. Strategy of backup - 9.3. Types of tape readers - 9.5 REV Iomega - 9.4. Safeguards on hard disk (NAS - SAN)

9.1. Introduction.

This chapter treats methods of safeguard of the servers data (back-up). If they are obsolete for the office computer, the tape readers are the essential elements of the storage in network. The technology of these tape readers passes by speed transmissions up to 200 MB/s with capacities active until Tetra (1000 GB).

Hard disks servers connection in RAID gets a pretence of safeguard, or rather a false sense of security. In the world networks, if the data of the discs can be recovered under certain conditions (RAID 1, RAID 5), an attack by virus, a malevolent intrusion or the flight of a computer directly involve losses of data and production. In the case of a PC "stand alone" (not connected in network) of professional use, the conservation of the data at all costs had been largely detailed in the course of first.

In the case of the discs servers, the problem is equivalent into worse. Firstly, the users make whole confidence with the network (and especially with the network administrator) for the data backups. Indeed, the safeguards are normally daily on the servers. Secondly, the networks applications are often too large to be individuality safeguarded (place, access...)

An essential point in the safeguards lies in the use by the users or other programs of the files all confused types. It is of primary importance that users leave the network when they leave work. If a file is used by a station, it will not be safeguarded. With the types RAID 1, we saw that we can cut hard drives of the users. Discs is thus accessible in read/write for the users while second is used only by the system of safeguard. When the backup is finished, the 2 discs are resynchronizes and the system RAID returns in operational mode 2 hard disks.

9.2. Strategy of backup.

Whatever examples to show the importance of a daily safeguard.

1. tackle virus or intrusion by Internet (hacker)
2. modification of the configuration software directly on the server (method largely used in practice) to add functionalities and... faulty operation. In practice, oblige the programmers to make a complete copy of the file on the hard disk. It is faster in the event of problem and will avoid you hours of recovery on tape.
3. accidental or different obliteration of files, losses of files in the contents of the disc.

In these three cases, the discs in RAID are not useful to you with nothing.

9.2.1. In first, we had seen the three types of safeguard:

Complete backup : save the whole of the files of the hard disk. This safeguard is very sure, but long.

Incremental backup: safeguard only the files which were modified since the last safeguard. A restoration thus requires to recover a complete safeguard initially and then to take again the incremental restorations.

Differential backup : copy all the files since the last backup complete or incremental. Indeed, this mode of safeguard does not modify the bit of file of the files. 

Each method has its qualities and its defects. It should not be forgotten that the duration of a back up is long, from where the interest not not to save too much. Moreover, one daily complete safeguard would make double function, the programs and the operating system is seldom modified every days.

The complete backup makes it possible to take again the whole of the files of only one block. Nevertheless, in the event of complete loss of a hard disk, it is initially necessary to reinstall the operating system. The duration of a complete backup is very long and obliges to cut the servers of the users. Indeed, in recovery, one replaces the files completely. If a file misses, the program does not function or worse will pose "odd" problems.

An incremental saves the files which are not safeguarded yet. Consequently, these safeguards are fast. But... The recovery of the files of an incremental safeguard obliges to recover some several behind, until a complete safeguard of the file.

A differential saves all the files since the last complete or incremental backup. The time of safeguard is thus very long and increases with each safeguard. As the bit of safeguard is not notched, one needs another type of front safeguard. If not, the server (or the file) will be completely safeguarded each time

Let us mix the methods of safeguards with the particular aspect of the use of the data on the server. The strategies below can be complete on the disc or by part (files). Moreover, it can be mixed.

A strategy of interesting safeguard of the data remains a followed regular complete safeguard of a safeguard differential day. Unfortunately, this poses two problems. The first is the periodicity of a complete safeguard. The longer it is, the more the differential backup will take time. And the second is precisely the duration of a differential backup.

A second consists in making a complete backup per month, follow-up of an incremental backup per week and a differential per week. This strategy is flexible, but requires the use of many sets of different bands.

A third consists in making a complete backup system per month, a differential backup on the files important each day and an incremental daily newspaper on the other files (documents users). This strategy seems the best but it obliges each day to start two backup different. Indeed the programs of safeguard are generally not conceived to mix at the same session two types of backup. You can nevertheless write on the same daily tape the differential file and the incremental file.

A last thing concerning the use of the bands. Change band every days. The bands must be duplicated. An even series and an odd series. In this manner, if a band of Monday is defective, that of previous Monday will not be it. The plays of safeguard should not be in the same part (and even in the same building) as the server. Think of the flight or fire hazards for example.

9.2.2. Example of office automation strategy of safeguard

Here an example of strategy of backup in an office automation system. In this case, the applications do not turn night, from where interest to make the safeguards during this period. 

In our case, the backup of Friday is a differential. It can be replaced by that of Saturday if there are no activities saturdays in the company. This avoids a displacement of the personnel for... changing the bands.

9.2.3. Industrial example of strategy backup

We leave the case here where the data-processing installation does not stop, with only one deceleration Sunday morning for example (maintenance of the production equipments). The problem in this case remains the users. What an administrator network without users would be happy.

The second problem in this case is the load on the server during the safeguard. While safeguarding, you slow down the system. The problems of the users is solved by the system RAID, but not the workload of the server during the safeguard. It is thus important to choose the hour of the safeguards, not at 8 hours of the morning when all the world starts.

The strategy of safeguard is done over 4 weeks, a complete safeguard of the system per month (4 weeks), all confused files.

The strategy resembles that office automation. RAID or not in week depends on the incidence of the safeguard on the work of the factory. Sunday takes again either a complete safeguard, or an incremental safeguard. This also depends on the incidence of the backup on the operation of the company. On the other hand, first Sunday of the month is a complete safeguard on 2 sets of bands with share.

It is necessary to find balance between safety, the duration of a safeguard and the incidence on the operation of the production equipments. Not question of stopping the factory two hours under pretext of safeguard data.

9.3. Type of tapes readers.

In first year, we already saw the backup on tape for the workstations. In the case of a station, the choices are multiple: diskettes (?), CD-writer, DVD-Rom, Zipp... and them bands... are used little. On the other hand, the bands make it possible to make a safeguard with the request without intervention of the user. This possibility, allied at the cost price of a band/MB makes it practically impossible to circumvent in the networks, it is practically only. This possibilities of the bands is combined to "chargers of band" who ensure of the capacities out of the common run. 

Technology QIC is not used any more in the safeguards networks, considering its too low capacity and speed of transfer. We interest this time Ci in two other types, DAT 4 and 8 mm and DLT. All these technologies are systematically interfaced in SCSI.

9.3.1. Safeguard DAT

The DAT was with the departure developed for the digital audio cassettes, with an audio quality CD. In 1998, HP and Sony defined standard DDS (DIGITAL Data Storage) on the basis of these cassette. Technology DAT in 4 cassettes of 4 mm employs a technology known as elliptic. It is the same type as that used in the video cassettes. It is of itself slower than the linear type. For this reason, this type of writing is generally used when large capacities are wished.

The writing is done by groups of 128 KB with a correction of error. At the time of the restoration, the band reads the entirety of the group (including the correction) before writing the data on the disc.

DAT data cartridges  exist in 2 formats: DDS and Data DAT. System DDS is most current.

9.13.2. Cartridges 8 mm.

The cartridges 8 mm were developed with the beginning for the videos: transfer of images in high color quality on tape for safeguard. Similar with the DAT, but generally of larger capacity, the 8mm also uses helicoids technology.

Two standards are currently used according to the system of compression: Exabyte Corporation and its standard 8 mm and the mammoth developed by Seagate and Sony.

For recall, the MTBF is Mean Times between Failures, average time between two breakdowns.

9.13.3. The DLT

Developed in the years 1980 by DEC (DIGITAL, repurchased by Compaq) for its microcomputers VAX, technology DLT really appeared in 1989. This technology was repurchased in 1994 per Quantum. Other manufacturers use this technology in OEM. 

Reader DLT use a cartridge smaller than the bands 8mm. The data are written on parallel tracks grouped per pairs. Each track uses the entirety of the band. When the end of the track is met (run-out), the heads are repositioned on a new pair of tracks and the safeguard continues while returning by the back) until the band is complete (by going - return). The current bands include 128 or 208 tracks.

Technology DLT is single in the establishment of the heads. The 6 guide installation of ensures a helicoids unfolding of the band (as well as technologies above), ensures an excellent contact bandages/head this is associated 2 guides which make only the cleaning of the band and are not motorized. This ensures one lifespan of the 30.000 hour old heads, for 2000 in the case of the DAT

9.13.4. Super DLT

The Super DLT backup are also provided by Quantum. These bands increase the capacity of bands DLT. In this case, the heads are controlled by laser beam (LGMR).

9.13.5. LTO (Linear Types Open)

Destined to replace SDLT, technology LTO allows a capacity of 200 MB (400 MB compressed for LTO-2) with a maximum speed of 144 GB/hour for version LTO-2 HH and until 245 GB/hour for standard version LTO-2. The last version LTO-3 allows until 800 GB in compressed mode with a transfer rate of 490 GB/hour. 

These safeguards on tapes include various mechanisms of heads protections, adaptation of writing/reading speed according to the speed of transfer towards the waiters.

9.13.6. Libraries

The chapter would not be complete without mentioning the libraries. They are tape readers including several bands established in an external charger (as in the CD chargers) or provided with a drawer by band. 

If they can be established as solution standard backup, their principal use consists in filing the data which (or not often) are not employed too much. The data are recognized as forming part of the hard disk but are not physically stored above. When you read such a file, it is taken again starting from the bands to be transferred on the disc. At the end of the day generally, the program takes again all the files not used for a certain time to insert them on the tapes. The bookshop thus makes function of disc at low prices.

A similar solution is established under Netware Novell which compresses the files the least most often used on the hard disk, increasing the disk space to decompress them in the event of use.

9.4. REV from IOMEGA

Developed to replace the backup DAT tapes and Jazz readers, the REV of Iomega has many advantages. Does reader REV use removable cartridges of 35 GB (90 GB compressed) that is to say the largers capacities of readers DAT. Internals, REV are interfaced in IDE, SATA or SCSI. In all cases, the maximum speed of transfer is 25 MB/second. The REV are also available in external version (interface SCSI, Firewire (Mac) or USB). The safeguard software associate give the same functionalities that standard bands. The large advantage comes from the price of this equipment, near 400 € (half of DAT reader price) even DAT are generally interfaced in faster SCSI 160. It is the current solution for the backup of small file servers, even if the price of DAT cartridge are cheaper that REV storage media (50 € approximately)

9.5. San and NAS

9.4.1. Introduction.

We saw the data storage on the hard disks of the servers. This solution implies a dedicated server which finally makes only distribution of files. This distribution of files causes an extra work of work on the server. Moreover, the price of the licenses servers is expensive. Other solutions of storages make it possible to occur from server.

9.4.2. NAS (Network Attached Storage).

A NAS consists of one or more hard discs generally assembled in IDE (RAID or not), of an interface RJ45, an electronics of the computer type (microprocessor, memory, wearing of input/output) and of an often priority operating system (specific to the apparatus) of Linux type. The exploitation itself is done by the intermediary of a station and of a Web. navigator the administration consists in parameterize the rights of access of the users, parameterize parameters TCP/IP and server DHCP generally included. In short nothing complex good. It is precisely the strong point of these apparatuses, the simplicity of implementation and the price (not of Windows license).

Like option for these apparatuses, let us quote the discs Hot Plug (extractable hot), systems RAID, discs SCSI, synchronization of the rights of access with the privileges users existing on the server.

Like all apparatuses networks, one will find redundant power supply ...

9.4.3. SAN (Storage attached Network).

As for the NAS, the discs are not attached to the principal server of the network. In this configuration, discs and libraries of band are directly connected to a network of storage Fiber Channel. Normally, all the discs and libraries of band are visible by all the processors. The functionality of Zoning makes it possible to isolate from the sets from discs and libraries of the other sets. In the case of the NAS, the discs are thus not regarded as pertaining to only one server. Nevertheless, to the difference of the NAS, the management of the files is entrusted to the servers. This can pose problems in the case of two servers of different operating systems.

The difference between a SAN and a NAS thus rests primarily in positioning on the network. On the other hand, the implementation of a SAN is definitely more complex.

1. Network course - 2. Introduction to communication - 3. Base of transmission -  4. Ethernet - 5. Switch, router, ... Ethernet - 6. Internet connections - 7. Networks servers - 8. SCSI, SAS, RAID - 9. Backup Tape drives, NAS, ... - 10. Hardware Security - 11. Wireless and Wifi - 12. UPS, Inverter, Power Supply - 13 . Corporate network - 14. Alternative technologies - 15. Touch Screen, video projector 17. Exercise: connecting hardware ADSL firewall

Hardware 1 course: PC and peripherals, Hardware 2 course: Network, servers and communication.

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