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raid.html
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 37  <article class="site-post">
 38     <header class="post-header">
 39        <h1 class="post-title">RAID</h1>
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 58  
 59  <p>
 60      RAID, or Redundant Array of Independent Disks (previously called
 61      "redundant array of inexpensive disks"), is a
 62      storage technology that combines multiple physical disk
 63      drives into a single logical unit for the purpose of data
 64      redundancy, performance improvement, or both. There are several
 65      RAID levels, each with its own configuration and benefits.
 66      It was invented by David A. Patterson, Garth A.
 67      Gibson and Randy H. Katz, in 1987.
 68  
 69  </p>
 70  
 71  <p>
 72      In a RAID array, data is distributed or replicated across
 73      the member drives according to the chosen RAID level. The
 74      two primary categories of RAID configurations are
 75      mirroring and striping.
 76  </p>
 77  
 78  <p>
 79    NOTE: RAID can increase data security, but it is not a backup.
 80  </p>
 81  
 82  
 83  
 84  <span style="color:#ff6600">
 85      <h1 style="font-size:25px">Hardware / Software RAID</h1>
 86  </span>
 87  
 88  
 89  
 90  <span style="color:#ff6600">
 91      <h1 style="font-size:20px">Hardware RAID</h1>
 92  </span>
 93  
 94  <p>
 95      In hardware RAID, a special controller
 96      takes care of the RAID tasks, and it's often
 97      part of the storage system. This controller has
 98      its own processing power, which can make it faster,
 99      but it can also be more expensive. This is what
100      a hardware RAID controller looks like:
101  </p>
102  
103  <img style="max-width:95%; width: 500px;" id="img_DocPreview" src="raidcontroller.jpg"/>
104  
105  <p>
106      Setting up hardware RAID is done through a dedicated interface
107      or tool from the RAID controller, similar to accessing the BIOS.
108      When it comes to moving RAID configurations to a different system,
109      hardware RAID can be trickier because it depends on a specific
110      RAID controller.
111  </p>
112  
113  
114  
115  <span style="color:#ff6600">
116      <h1 style="font-size:20px">Software RAID</h1>
117  </span>
118  
119  <p>
120      Software RAID is generally more flexible and can be
121      moved between systems with compatible software support.
122      Software RAID is managed directly through the operating system.
123  </p>
124  
125  <p>
126      Unlike hardware RAID, which has its dedicated processor,
127      software RAID uses the computer's CPU and RAM for RAID calculations. While this
128      may cause a slight overhead, modern CPUs are
129      mostly powerful enough to handle these tasks efficiently.
130  </p>
131  
132  <p>
133      Software RAID configurations can be easily adjusted and managed
134      through the operating system's tools. This flexibility allows
135      users to create, modify, or delete RAID arrays without the
136      need for specialized hardware or additional components.
137  </p>
138  
139  <p>
140      One of the primary advantages of software RAID is its cost-effectiveness.
141      Since it relies on the existing resources of the host system, there is
142      no need for a separate RAID controller, making it
143      a more budget-friendly solution.
144  </p>
145  
146  
147  
148  <!-- --------------------------------------------------------------------------------------------------------------------------------- -->
149  
150  <span style="color:#ff6600">
151      <h1 style="font-size:25px">RAID Levels</h1>
152  </span>
153  
154  <p>
155      Each RAID level serves different purposes in terms of performance,
156      redundancy, and capacity. Here are the most common RAID levels:
157  </p>
158  
159  <!-- --------------------------------------------------------------------------------------------------------------------------------- -->
160  
161  
162  <hr>
163  <span style="color:#ff6600">
164      <h1 style="font-size:20px">RAID 0 (Striping)</h1>
165  </span>
166  
167  <p>
168      Pro: High performance, no overhead.
169  </p>
170  
171  <p>
172      Contra: No redundancy.
173  </p>
174  
175  <p>
176      A minimum of 2 physical disks needed.
177  </p>
178  
179  <p>
180      Usable capacity: n-0
181  </p>
182  
183  <p>
184      Failed drives without data-loss: 0
185  </p>
186  
187  <img style="max-width:95%; width: 500px;" id="img_DocPreview" src="RAID0.jpg"/>
188  
189  <!-- --------------------------------------------------------------------------------------------------------------------------------- -->
190  
191  
192  <hr>
193  <span style="color:#ff6600">
194      <h1 style="font-size:20px">RAID 1 (Mirroring)</h1>
195  </span>
196  
197  <p>
198      Pro: Instant failover: If the primary drive fails, the secondary
199      can be accessed directly, preventing data loss.
200  </p>
201  
202  <p>
203      Contra: Twice as much storage capacity required. Write speed is
204      slow as data is written to two hard drives at the same time.
205  </p>
206  
207  <p>
208      A minimum of 2 physical disks needed.
209  </p>
210  
211  <p>
212      Usable capacity: n-1
213  </p>
214  
215  <p>
216      Failed drives without data-loss: 1
217  </p>
218  
219  <img style="max-width:95%; width: 500px;" id="img_DocPreview" src="RAID1.jpg"/>
220  
221  <!-- --------------------------------------------------------------------------------------------------------------------------------- -->
222  
223  
224  <hr>
225  <span style="color:#ff6600">
226      <h1 style="font-size:20px">RAID 5 (Striping with Distributed Parity)</h1>
227  </span>
228  
229  <p>
230      Pro: High security through distribution of parity data across
231      all hard drives: Hard drives can be replaced
232      during operation (aka. are hotswappable).
233  </p>
234  
235  <p>
236      Contra: Write speed is slow.
237  </p>
238  
239  <p>
240      A minimum of 3 physical disks needed.
241  </p>
242  
243  <p>
244      Usable capacity: n-1
245  </p>
246  
247  <p>
248      Failed drives without data-loss: 1
249  </p>
250  
251  <img style="max-width:95%; width: 500px;" id="img_DocPreview" src="RAID5.jpg"/>
252  
253  <!-- --------------------------------------------------------------------------------------------------------------------------------- -->
254  
255  
256  <hr>
257  <span style="color:#ff6600">
258      <h1 style="font-size:20px">RAID 6 (Striping with Dual Parity)</h1>
259  </span>
260  
261  <p>
262      Pro: Double parity protects against data loss.
263      The percentage of usable data storage increases
264      as more hard drives are added.
265  </p>
266  
267  <p>
268      Contra: Lower performance than RAID 5.
269  </p>
270  
271  <p>
272      A minimum of 4 physical disks needed.
273  </p>
274  
275  <p>
276      Usable capacity: n-2
277  </p>
278  
279  <p>
280      Failed drives without data-loss: 2
281  </p>
282  
283  <img style="max-width:95%; width: 500px;" id="img_DocPreview" src="RAID6.jpg"/>
284  
285  <!-- --------------------------------------------------------------------------------------------------------------------------------- -->
286  
287  
288  <hr>
289  <span style="color:#ff6600">
290      <h1 style="font-size:20px">RAID 10 (Striping and Mirroring)</h1>
291  </span>
292  
293  <p>
294      Pro: Good performance and fault tolerance. It combines striping and
295      mirroring to provide both speed and redundancy.
296  </p>
297  
298  <p>
299      Contra: Twice as much storage capacity required.
300  </p>
301  
302  <p>
303      A minimum of 4 physical disks needed.
304  </p>
305  
306  <p>
307      Usable capacity: n-2
308  </p>
309  
310  <p>
311      Failed drives without data loss: Half of the total drives can fail without data loss.
312  </p>
313  
314  <img style="max-width:95%; width: 500px;" id="img_DocPreview" src="RAID10.jpg"/>
315  
316  
317  <!-- --------------------------------------------------------------------------------------------------------------------------------- -->
318  
319  <p>
320      Each RAID level has its own advantages and trade-offs,
321      and the choice depends on the specific requirements
322      of the application, including considerations for
323      performance, data protection, and available
324      storage capacity.
325  </p>
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