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Partitioning and Formatting

If you purchase a drive and interface from APDL or have it fitted by a dealer it should be ready to use. If you supply your own drive you will need to format it and you may wish to partition a drive even if it is already formatted so you should read this section.

Note that drives are normally supplied with a standard E format. If you are using RISC OS 4 and want to use the E+ format with long filenames you will need to re-initialise the drive before you copy any data to it.

3.1 What are Drive Partitions?

The ideA system supports drive partitions. This is nothing to do with 'PC partitions' used by PC cards or emulators and alternative operating systems like Linux and RISC BSD but a way of dividing up a large 'physical' drive into several partitions or 'logical' drives. There are three reasons why you may want to do this.

  1. With operating systems before RISC OS 3.6 the maximum drive size permitted is 512 Mb. Chopping up bigger drives into a series of partitions enables large drives to be used on earlier OS's.
  2. Each partition can be protected by a password. This is useful if more than one person uses the computer or if you have confidential data on your hard disc.
  3. On very large drives the Large File Allocation Unit (see later) rises which makes storing large numbers of small files on the drive very wasteful of space. Dividing the drive into several partitions reduces the LFAU.

Before proceeding it is necessary to define the terms physical drive and logical drive .

A physical drive is an actual hard disc. As has already been explained up to four of these could be connected to an ideA interface.

A logical drive is a drive as it appears to the operating system and to the user. ie. in the RISC-OS desktop it's a drive icon on the icon bar. The ideA filing system supports up to eight logical drives so you could have up to eight ideA drive icons. This is far more than would normally be required but it does allow very large drives to be fitted to pre RISC OS 3.6 machines or a mixture of large fixed hard discs and removable drives.

3.2 Large File Allocation Unit (pre RO4)

This is not the place to go into the technicalities of data organisation on drives, so what follows is a simplification and intended to illustrate why this is pertinent. The LFAU can be considered as similar to Sector Size on a floppy disc. When a file is saved to floppy disc it must start at the beginning of a sector, so unless its length is an exact multiple of the sector size there will be space left over at the end of the file before the next file can begin. On small hard drives the Allocation Unit is only 512 bytes, so not much is wasted, and with drives less than 499Mb it's still only 1K. However, as the drive size doubles so does the LFAU. Above 499Mb it's 2K, at 998Mb it rises to 4K, 1996Mb 8K and at 3996Mb 16K. If you have mainly large files or big image files on your drive the wasted space will not be significant, but if you have many small files or applications there can be a lot of wasted space since the wasted bit at the end of each files gets larger as the LFAU gets bigger.

The LFAU is unimportant with versions of RISC-OS less than 3.6 as these do not allow drives larger than 512Mb, but with later machines it can become significant.

One way of getting around the problem is to use Image Files created with programs like ArcFS, David Pilling's SparkFS or the Public Domain X-Files. These let you put lots of small files into a single large file on the hard disc. The other solution is to divide a large physical drive into two or more logical drives, each of which will have the LFAU commensurate with its size.

For example, you could divide a 4Gb drive into three logical drives. Two just under 1Gb for 'normal' use (these would have a LFAU of 2K, which is reasonable) and one 2Gb which could be used for large files like a PC 'partition' file, big graphics files, etc.

Exactly how you organise your drive will be a matter of personal preference, but remember that you cannot alter the size of partitions without re-initialising the whole drive, and this will destroy all the data on it. So think carefully first, it can be a major operation to reorganise a drive once you have filled it!

3.3 RISC OS 4 and partitions

RISC OS 4 has a much improved system for allocating space on hard drives so most of what has been said about LFAU no longer applies. However, there are still many reasons why you might want to partition a drive. The password protection system available with ideA lets you protect individual partitions so you could create a partition to use just for confidential data. Alternatively you may prefer to divide a large drive into sections simply because it helps you to organise your data. If the computer is connected to a network or is acting as a file server you can make some partitions 'visible' to the network and others only available on the host machine.

3.4 Partitions and other filing systems

If you move a drive that has been formatted and partitioned on an ideA interface to another filing system then only the first partition will be seen by the other filer. For example, if you partition a drive on an ideA interface and then move it to the same or another computer and connect it directly the the built in IDE controller then only one drive icon will appear representing the first partition. This can be used perfectly normally, but there is no way of accessing any other partitions.

If the drive is returned to an ideA card all the partitions will re-appear.

This is not normally important, but it should be borne in mind if you are formatting removable media drives, although it is not normally recommended that you partition these.

3.5 Using the IDEFormat program

This is supplied on a floppy disc with your interface. It may be best if you do not copy it to your hard disc, especially if other people use the machine, to make sure that it isn't run by accident as many of the operations will wipe out all the data on the drive.

Although it is called formatting modern drives are actually formatted by the manufacturers and all that is necessary is to write the Boot Block, Map, Root Directory structure and other essential data to the drive. This is called 'initialising' and takes only a couple of seconds.

When you run the program if you have more than one drive it will ask you which PHYSICAL drive you wish to operate on. This will be a number 4 to 7. It will then display the characteristics of the selected drive. If you have more than one drive check that this is actually the drive you want to format. You will then see a menu with the following options -

   1.    Add new partition to table
   2.    Delete partition from table
   3.    Edit drive parameters
   4.    Change drive interleave
   5.    Clear bad blocks
   6.    Initialise all drive partitions
   7.    Initialise ONE drive partition

   9.    End

3.6 Formatting a drive

I will describe the process of initialising a new, unformatted, 850Mb drive with two partitions, one of 320Mb and one using up the rest of the available space.

First select Option 1. The program will inform you how much space you have available to allocate, and with an 850Mb drive this might be something like 812 Mb (drives sizes are nominal). Enter the size of the first partition, 320, and press RETURN. You will be told that you have 492 Mb available (812 minus 320). Enter 492 and press RETURN again. You will now be told that you have 0 mb left (it's all been used up) so just press RETURN and the menu will come back again.

Now select 6 to initialise the drive partitions. You will be asked if you want the drive to be 'bootable'. If you intend IDEFS to be the default filing system answer 'Y', if you intend it to be a secondary filing system (eg. on a RiscPC) you can answer 'N'. As each partition is initialised the program will pause to inform you of the LFAU for that partition. press RETURN at this point and it will carry on. This is for information only, you can't alter this figure (except with RO 4, see later). When the menu re-appears, select 9 to finish.

When you return to the desktop it is best to press RESET or CTRL-BREAK to restart the computer, especially if you have altered the number of partitions on the drive. In this example you would now find that you have two IDEFS drive icons for the drive. These have been given default drive names by IDEformat, probably IDEDisc4 and IDEDisc5. You can change them from the drive menus if you wish. The drive is now ready to use.

If you had wanted to have just a single logical drive you would have entered the full drive size for the first partition.

Warning If your computer is fitted with an OS less than 3.6 do not attempt to create a partition greater than 511Mb . IDEformat may appear to create and initialise the partition but it is larger than the maximum permitted for these machines and will cause serious problems as the drive fills up with almost certain loss of data.

Sometimes with drives over 2Gb previously formatted under another system some parameters may be wrongly interpreted and drive size or free space appear as negative numbers. If this happens select option 3, Edit drive parameters, before you attempt to create partitions or initialise them. IDEformat will read the correct parameters from the drive and offer them to you to alter. Just press RETURN to accept the default values offered and this will automatically correct any errors.

3.7 Use with RISC OS 4

The only difference when initialising a drive with RISC OS 4 is that you will be offered the option of using the new 'E+' disc format which permits long filenames. and unlimited files per directory. You will see a message asking 'do you want to use long filenames'. If you answer 'N' then the drive will be formatted to the 'old' system. If you choose the new E+ format you will also have the advantage of the much more efficient disc space usage that the new format allows. However, it will not be possible to read the disc on any machine not using RISC OS 4. This is most unlikely to matter with a fixed hard drive, but with removable media it would probably be best not to use the new format to ensure compatibility.

As the LFAU is not fixed with the new format you can alter it if you wish. In theory a larger LFAU may speed up large file data transfer slightly at the expense of less efficient use of drive space. Unless you know what you are doing it is probably best to just accept the default figure offered.

If you get an error message with a small LFAU then try again with the next size up. For example, if the error was generated with 512, try 1024, if with 1024, try 2048. This may happen because if the calculations are 'borderline' the formatter may offer a size which is slightly too small.

3.8 Deleting a partition

This option is used to remove a partition. If a drive has been formatted and you wish to change the number or size of the partition(s) you will have to use this to remove the old partitions before you can install the new one(s). Note that altering the partition table normally means you will have to re initialise the drive and lose all the data on it.

It is possible to remove the LAST partition in the table without affecting data on the other partitions. It is also possible to add a partition or partitions to use capacity which had not previously been allocated, eg. on a machine with a partition size limit of 512Mb and a drive which has more capacity than required at present you could add partitions as you fill up the drive to avoid having any more icons than necessary.

Removing any but the last partition will scramble the partition table and could mean that you will have to re-format the entire drive.

3.9 Clear bad blocks

This will verify the drive and swap any blocks which return errors with spare blocks. It should not be necessary on a new drive but you may wish to do it if you are fitting an old or secondhand drive.

This can take quite a while, particularly with a large drive.

3.10 Edit drive parameters

This is used to change the drive parameters from the standard values for the drive. Unless you are sure of what you are doing do not alter these.

3.11 Change drive interleave

Almost all modern drives are set to use 1:1 interleave and this will be suitable for most computers. On older machines or with very old drives it may be possible to speed up data transfer by altering the interleave, but unless performance is disappointingly slow it is unlikely that it will have any effect. With most drives this will completely wipe all data from the drive so you will need to repartition and initialise it.

3.12 Initialising a single partition

Normally you would only initialise partitions when you first install a drive, and you would then need to initialise them all. However, there may be times when you would want to initialise just a single partition, for example, if you no longer want any of the data on a partition then it is quicker to re-initialise it (wiping out all the files) rather than deleting them, or you may have a 'broken directory' which can be difficult to remove by other means.

When using this option be absolutely sure you are selecting the correct partition to initialise. If you choose the wrong one you will be unable to recover the data. Partitions on each individual drive are identified by number, starting at 1. To equate this to the drive icon, partition number 1 would be the right hand icon for that physical drive , number 2 the next icon to the left, icon 3 the next, and so on.

3.13 Drive names

As has already been described you can set the name of each drive or partition from the drive menu. Each drive must have a unique name or the computer will be unable to distinguish between them and you will constantly get 'Ambiguous disc name' errors.

Warning . Because of a bug in the desktop 'Free' you should not give a drive or partition a name with four characters.

3.14 Formatting removable media drives

Discs in these drives are initialised just like any other hard discs, but it is best if they do not have multiple partitions as this can cause difficulties when discs are changed.

If you have a large removable media drive on an older machine then although not recommended, you can partitions the discs, but you must partition every disc in the same way or the filer will become very confused when you change discs.

The IDEFormat program assigns a drive name based on day, time and partition number on removable media drives to ensure that removable discs have unique names.


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