From 01ccf39090253106c9026c589900eac295f2603e Mon Sep 17 00:00:00 2001 From: "Martin A. Brown" Date: Tue, 2 Feb 2016 09:13:44 -0800 Subject: [PATCH] uppercasing the Storage in the name (matching to output tree) --- ...-Mass-storage-Definitions-Naming-HOWTO.xml | 609 ------------------ 1 file changed, 609 deletions(-) delete mode 100644 LDP/howto/docbook/Partitions-Mass-Storage-Definitions-Naming-HOWTO/Partitions-Mass-storage-Definitions-Naming-HOWTO.xml diff --git a/LDP/howto/docbook/Partitions-Mass-Storage-Definitions-Naming-HOWTO/Partitions-Mass-storage-Definitions-Naming-HOWTO.xml b/LDP/howto/docbook/Partitions-Mass-Storage-Definitions-Naming-HOWTO/Partitions-Mass-storage-Definitions-Naming-HOWTO.xml deleted file mode 100644 index bec78963..00000000 --- a/LDP/howto/docbook/Partitions-Mass-Storage-Definitions-Naming-HOWTO/Partitions-Mass-storage-Definitions-Naming-HOWTO.xml +++ /dev/null @@ -1,609 +0,0 @@ - - -
- - - Jean-Daniel - Dodin - -
- jdd@dodin.org -
- - - - Partitions-Mass-Storage-Definitions-Naming-HOWTO - - - V0.1 - 2009-05-09 - jdd - - - - -
- - - Partitions-Mass-Storage-Definitions-Naming-HOWTO, - copyright (c) 2009 Jean-Daniel Dodin -
-
- Copyright and Licence - The copyright of this document is to the author, - Jean-Daniel Dodin, according to the following licence. - - - - - - GNU Free Documentation License - -
-
- Mass Storage Involved Here - Mass storage involved in the present HOWTO are rewritable - random access ones. Most of them are magnetic rotating disks - (floppies, Hard Drive) or flash memory (USB key or any kind of - memory card). - For example, cdroms and dvds are - notconcerned by this HOWTO ( - see - Wikipedia). Tapes are not either. - Mass storage are used by the kernel, so the basic doc can - be found on - - the kernel Web site - Reference site should be - the International Disk drive - Equipment and Materials Association. - Shouldbecause this Web site is not very - friendly. -
-
- Definitions -
- Warning - Many definitions about drives are only virtual. That is - they are used, but the hardware is often quite different from - the expected description. Usually this have no odd result, - any mass storage have to be seen as a - black box. -
-
- Bytes - Computers counts with binaries, 1 & 0, - 1111100001110... To be able to read this better, humans uses - nibbles (4 bits) often shown as Hexadecimal numbers from 0 to - f (0123456789abcdef). Nibbles are usually grouped by two and - this gives a byte. The most used memory unit is byte and it's - multiples, KiB (Kilo Bytes), MiB (Mega Bytes), GiB - (Gigabytes). The "i" denotes the binary use (0ne Ki is 1024, - not 1000), the uppercase "B" denotes Bytes, not bits. -
-
- Sectors - Sometime, the word - blockis used in place of - sectors. - Mass storage devices (at least the ones we are dealing - with here) store bytes in "Sectors" of 512 Bytes. This is - uneven, because any sector count have to be divided by two to - have the KiB number, so most partitonning software accepts - letters k (KiB), m (MiB), g... as options. Wise ones do not - make any case difference. - Sector size is the available byte count. The true - sector is bigger, as it have to include housekeeping data. - You don't have to worry about that. - Notice that as of 03-22-2006, the IDEMA annouced a new - sector size of 4kiB (4096 Bytes): - - - doc file, can be openned with OpenOffice.org. -
-
- Heads - Rotating mass storage devices uses - heads. True heads are the physical - electromechanical device that writes and read the magnetic - track. Drives being made of rotating plates, the plates have - two sides, so disks can have two head by plate. Having two - plates (frequent) you have four heads. - Heads are writing through very complex system, see - detailed info here: - . -
-
- Tracks - Plates are rotating. When a head is still, the plate - rotation and the width of the head are defining a - track. - Heads are moving from the external part of the plate to - the inner part, step by steps. Each step defines a new - track. -
-
- Cylinders - Heads are moving together, all at the same time. They - may rotate - on they own center, not the plate center, of - course. They also may have a linear move. You can see an - example of linear moving head in any cdreader, looking at the - move of the laser head. Most disks are as shown by this - wikipedia image - . - When you think of all the tracks defined by each head - at the same time, you have a cylinder. So on a rotating - drive, all the tracks of the same cylinder are read or - written at the same time. The actual data is spread on all - the plates. The way the data is actually written is up to the - drive manufacturer, not the user. -
-
- Disks - Small disks are used directly as a hole bunch of - sectors. Basic programs can access data directly on sectors. - Many do (like dd or any partitionning programm). - But we live in a world of extremely high capacity mass - storage. Terabytes is normal nowaday (2009), when a complete - Linux system can live on a floppy (1440 bytes). So there is a - need of making several parts from a mass storage device, - though the partitions. -
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- Partitions - Partitioning is a means to divide a single drive into - many logical drives. A partition is a contiguous set of - sectors. To lessen the heads travel, partitions can be - "aligned" on the cylinder size, that is use an integer number - of cylinder. This is not always done, but should as it have - many other advantages for recovery. -
-
- Partition Table - As you can have many partitions, you need to have a - partition table. This partition table is stored in the very - beginning of the drive. It's very unlikely that you will have - to change this table directly writing bytes with an - hexadecimal editor, so we wont say more on the position of - the table. - There are many Operating Systems all around that all - share similar hardware and as many partition systems. We will - look only at what one can find in a PC, even if it's not easy - to define that nowaday. Say, for us, a PC is any computer - able to run Linux (I know, it's not always true). - Each of these partition kinds are noted in the table by - a special flag called "type" ("t" in fdisk). Most known are - type 83 for Linux partitions and 82 for Linux swap (hex - numbers). - Notice that most Operating Systems can share partition - tables. At least, if a disk is hardware compatible with - several systems, these systems should be able to see what the - others have done, not to erase a drive by accident. I can't - say for sure that its true in the real life. -
-
- File Systems - Partitions can be accessed directly as sectors, as any - part of the disk, but are usually filled with a - file system. File system - and partitions are related only because a file system is in a - partition, but that's all. You can have a disk without - partition but with a file system or have partitions without - file system (the swap partition beeing the most well known). - For details on file systems, - see - Wikipedia. - In summary, file systems allow storing data in files - with human readable names and to sort the files in a friendly - way, for example as directories, subdirectories, text, - images... -
-
- Files and Nodes - Nearly all what you can find on a mass storage - partition, beside sectors, from an user point of view, is a - file. But computers are curious geeks and you can treat files - like disks if you want. Using the "loop" system, default in - most Linux kernels, one can partition the inside of the file, - create file systems on it and mount it. This is specially - handy for experiments. - Some of these files are - devicesor - nodes. Partitions are not files and are - accessed via special nodes we will see later. These nodes are - not created by touch but by - mknode. Use with caution. Nodes need a - type ( - cfor "character" or "b" for - block) and major and minor numbers. For - what we need, major numbers are disk numbers and minor - numbers are partition numbers. The list is visible in - /proc/partitions - - - - - - - Creates a /dev/sda9 node of no nuse, given this don't - create partition, only the node. In a usual Linux - distribution, nodes are dynamically created at boot time, so - nobody should have to do so. However, sometime the automatic - system fails. -
-
-
- Drive Naming in Linux - There is a special nomenclature that linux uses to refer - to mass storage that must be understood. -
- Naming Convention - Linux used to deal with two kind of drives, depending - of the electronic interface (controller), IDE and SCSI. - Oldtimers remember the day where cdwriters where acccessed - through "SCSI emulation". In fact IDE and SCSI use mostly the - same low level commands and for 2007 up, with the new "SATA" - interface, the naming was unified and, in new ditributions, - all the drives have the same naming. For this part, CD or DVD - readers/writers are seen like Hard Drives. -
- Old IDE Names - By convention, IDE drives where given device names - /dev/hdato - /dev/hdd. - Hard - Drive - A( - /dev/hda) is the first drive and - Hard - Drive - C( - /dev/hdc) is the third. - A typical PC has two IDE controllers, each of which - can have two drives connected to it. For example, - /dev/hdais the first drive (master) on the - first IDE controller and - /dev/hddis the second (slave) drive on the - second controller (the fourth IDE drive in the - computer). - So, typically, a computer with IDE controller can - accomodate 4 drives: /dev/hda (primary master), /dev/hdb - (primary slave), /dev/hdc (secondary master), /dev/hdd - (secondary slave). Some (rare) Mother Boards have more than - two controllers, some addition cards can also have - controllers, these are numbered following the alphabet, but - one have to figure out what real names are given for his - particular hardware. - You can have drives where ever you want, it's not - mandatory to fill the gaps. You may have interest to read - about what drive/cdrom connect to what place, but it's out - of this document scope. -
-
- New Hard Drives Names - Now all the rotating hard drives uses the same names - as the old SCSI controllers, that is "s" in place of "h", - so /dev/sda, and so on. The number of drives depends on the - number of controllers on the Mother Board or the extended - boards. Usually 4 are available. What will be the number of - a drive is up to the controller card and the way it's read - by the kernel, so difficult to say at first. -
-
- Flash Drives Names - Flash drives are usually not connected through IDE or - SATA interfaces and so don't uses the same names. Several - interfaces are used with each different names. The kernel - documentations gives the names. -
-
- Low level Devices and Extra naming - You will find in some apps references to lowlevel - SCSI devices and various naming conventions, for example - (wodim is the command line cd burner): - - - - And you may have to use some sort of - SCSI:1,1,0option to access the CDROM. - try to avoid using this as much as possible, as it's very - error prone and should be let to programmers only. I only - mention it because you can't always avoid it. - If you do "cat /dev/ | more", you can see: - - sr0 -(...) -crw-r----- 1 root disk 21, 0 mars 9 07:56 sg0 -crw-rw----+ 1 root disk 21, 1 mars 9 07:56 sg1]]> - - These scd, sr, sg devices are lowlevel interface - (notice the "c" for "character"). Try not using them. - dmesgand - more /var/log/boot.msgshould give you - the usable sdxx device, like (short summary): - - sd 0:0:0:0: [sda] 976773168 512-byte hardware sectors: (500GB/465GiB) -<5>sd 0:0:0:0: [sda] Write Protect is off -<7>sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00]]> - - This mean the drive is - /dev/sda. - However these files (given by - dmesgand - more /var/log/boot.msg) used to be - easy to read but are no more. Now the kernel starts in - parallel several drivers, so the messages are mixed, you - can have - - sda:<6>USB Universal Host Contr'ller Interface driver v3.0]]> - - This don't mean that your sda drive is an usb one, - but the usb module was started at the same time as the - drive one and send it's messages simultaneously. You still - have a - /dev/sdadrive. -
-
- New Media Names - Here the dmesg content for inserting an USB - key: - - - - You see there all what we where speaking about right - now! SCSI emulation, scsi, sd and sg names, but also the - sdb that is most important for us. - Here are the messages for a high speed SDHC - card: - - - - When the two cards are probably the same flash memory - chip, the USB key uses the USB interface and SCSI - emulation, the SDHC card uses the PCMCIA slot of the - laptop, with a special device naming (/dev/mmcblk0). The - use, as far as partitionning is involved is the - same. -
-
- Disk ID - In a world where disks are many and removable, it's - impossible to track what device is used by what disk. So - there are now many way of using a disk name. This makes it - extremely difficult to work with basic tools. These are - "Disk labels" and "Disk UUID", also "Partition Labels". See - fstab man page for details. -
-
-
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- Partition Naming in Linux -
- Numbers - Partition naming is thanksfully simpler than drive one. - Partitions are simply given a number from 0 up (decimal). - Sometime a "p" is appended on front of the number: - - - - As you see, partition devices are listed in - /proc/partition. This file... is not a real file but is - created on the fly. Don't worry, for what we need it's a - file. - Notice the "p1" partition name for the SDHC - card. - Max number of partitions is 15 for SCSI and all the - drives using the new SATA driver, 63 for IDE drives (0 is the - full drive, 0 to 15 is four bits 0 to 64, 6 bits) -
-
- Meaning of the Numbers - Not all the numbers have the same meaning. This mess - come from the PC history. One can divide floppies with - partitions, but then 4 ones seems sufficient. But then come - Hard drives :-). So the partitons numbers 1, 2, 3 and 4 are - primarypartitions. One drive can only - have 4 primaries. - To go further, we have to use one of these primary as a - big one and sub-partition this one, so to have - logicalpartitions. The big - extendedpartition can be any of the - 4. - So, remember, the primary partitions are inside the - drive and the logical partitions are inside one of the - primary, called the - extendedpartition. - Once the logical partitions are created, it's no more - recommended to write directly to the extended one. Writing to - an extended partition would erase the logical ones like - writing directly to a hard drive erase the partitons. Beware, - - it's possible!! - If, after creating 4 primary partitions, all the disk - space is not used, the remaining space is lost (unusable), so - most of the time, create the desired primaries, then at last - the extended one with all the remaining room. - It's not necessary to create 4 primaries. You could use - only one extended (Linux only), but there are some advantages - of using primaries. - Primaries being 4, the first logical partition is - always 5. So any partition with number of five and up is a - logical one. -
-
-
- Device Major and Minor Numbers - The only important thing with a device file are its major - and minor device numbers, which are shown instead of the file - size: - - - - Shows permissions ( - brw-rw----), owner (root), group (disk), major - device number (8), minor device number (0), date (mars 9 - - french, no year), hour (07:56) and device name (guess - :-). - When accessing a device file, the major number selects - which device driver is being called to perform the input/output - operation. This call is being done with the minor number as a - parameter and it is entirely up to the driver how the minor - number is being interpreted. The driver documentation usually - describes how the driver uses minor numbers. -
-
- Partition Types -
- Linux Partition Types - A partition is labeled to host a certain kind of file - system (not to be confused with a volume label. Such a file - system could be the linux standard ext3 file system or linux - swap space, or even foreign file systems like (Microsoft) - NTFS or (Sun) UFS. There is a numerical code associated with - each partition type. For example, the code for ext2 is - 0x83and linux swap is - 0x82(0x mean hexadecimal). -
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- Foreign Partition Types - The partition type codes have been arbitrarily chosen - (you can't figure out what they should be) and they are - particular to a given operating system. Therefore, it is - theoretically possible that if you use two operating systems - with the same hard drive, the same code might be used to - designate two different partition types. OS/2 marks its - partitions with a 0x07 type and so does Windows NT's NTFS. - MS-DOS allocates several type codes for its various flavors - of FAT file systems: 0x01, 0x04 and 0x06 are known. DR-DOS - used 0x81 to indicate protected FAT partitions, creating a - type clash with Linux/Minix at that time, but neither - Linux/Minix nor DR-DOS are widely used any more. -
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- Swap Partitions - Every process running on your computer is allocated a - number of blocks of RAM. These blocks are called pages. The - set of in-memory pages which will be referenced by the - processor in the very near future is called a "working set." - Linux tries to predict these memory accesses (assuming that - recently used pages will be used again in the near future) - and keeps these pages in RAM if possible. - If you have too many processes running on a machine, - the kernel will try to free up RAM by writing pages to disk. - This is what swap space is for. It effectively increases the - amount of memory you have available. However, disk I/O is - about a hundred times slower than reading from and writing to - RAM. Consider this emergency memory and not extra - memory. - If memory becomes so scarce that the kernel pages out - from the working set of one process in order to page in for - another, the machine is said to be thrashing. Some readers - might have inadvertenly experienced this: the hard drive is - grinding away like crazy, but the computer is slow to the - point of being unusable. Swap space is something you need to - have, but it is no substitute for sufficient RAM. -
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- Complete List - From the fdisk help: - - - -
-
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- How Many Partitions - The exact number of partitions allowed on a drive is - fixed by the kernel. So you can find the exact number is the - kernel documentation, the last version is maintained here - If - you have the kernel source installed, you can find your version - on your computer at - /usr/src/linux/Documentation/devices.txt. - Look at "limit on partition". Find yours. Common SATA - number is 31, SCSI is 15, some are less. -
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