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1 e4rat reduces disk access times through physical file reallocation. It is based
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2 on the online defragmentation ioctl EXT4_IOC_MOVE_EXT from the ext4 filesystem,
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3 which was introduced in Linux Kernel 2.6.31. Therefore, other filesystem types
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4 or earlier versions of extended filesystems are not supported.
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5
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6 e4rat consists of three binaries. The first is e4rat-collect. Its purpose is to
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7 gather relevant files by monitoring file accesses during an application startup.
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8 The generated file list is the fundament of the second step. With the second
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9 step, e4rat-realloc, files are placed physically in a row on disk.
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10 The reallocation of the files' content yields a higher disk transfer rate which
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11 accelerates program start processes.
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12
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13 Third, you can also read-ahead files to gain a higher cache hit rate.
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14 e4rat-preload transfers files into memory in parallel to program startup.
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15
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16 Because a file consists of file content and its I-Node information the
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17 preloading process is divided into two steps. First, it reads the I-Nodes'
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18 information which are still spread over the entire filesystem. In the second
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19 step, the files' content is read without causing any disk seeks.
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20
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21 For more information see: e4rat-collect(8), e4rat-realloc(8), e4rat-preload(8)
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22 and e4rat.conf(5).
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23
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24
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25 SAMPLE USAGE: Accelerate the boot process
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26 -------------
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27
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28 Run e4rat-collect as init process through adding following line to Kernel
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29 parameters:
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30
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31 init=/sbin/e4rat-collect
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32
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33 After e4rat-collect has terminated the generated file list is stored at:
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34
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35 /var/lib/e4rat/startup.log
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36
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37 Before reallocating boot files it is recommaned to switch to runlevel 1 to stop
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38 most of all running proceses to gain write access to the process binary file:
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39
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40 init 1
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41
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42 Reallocating boot files:
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43
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44 e4rat-realloc /var/lib/e4rat/startup.log
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45
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46 To start e4rat-preload as initial process append following to kernel your
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47 parameters:
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48
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49 init=/sbin/e4rat-preload
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