|
Lines 362-368
Link Here
|
| 362 |
<sect2> |
362 |
<sect2> |
| 363 |
<title>Which Plex Organization?</title> |
363 |
<title>Which Plex Organization?</title> |
| 364 |
<para>The version of Vinum supplied with FreeBSD &rel.current; implements |
364 |
<para>The version of Vinum supplied with FreeBSD &rel.current; implements |
| 365 |
two kinds of plex:</para> |
365 |
three kinds of plex:</para> |
| 366 |
|
366 |
|
| 367 |
<itemizedlist> |
367 |
<itemizedlist> |
| 368 |
<listitem> |
368 |
<listitem> |
|
Lines 386-396
Link Here
|
| 386 |
(fractionally) more complex code and restrictions on |
386 |
(fractionally) more complex code and restrictions on |
| 387 |
subdisks: they must be all the same size, and extending a |
387 |
subdisks: they must be all the same size, and extending a |
| 388 |
plex by adding new subdisks is so complicated that Vinum |
388 |
plex by adding new subdisks is so complicated that Vinum |
| 389 |
currently does not implement it. Vinum imposes an |
389 |
currently does not implement it (actually, you have to reconstruct |
|
|
390 |
file system after adding or removing subdisks to the underlying plex). |
| 391 |
Vinum imposes an |
| 390 |
additional, trivial restriction: a striped plex must have |
392 |
additional, trivial restriction: a striped plex must have |
| 391 |
at least two subdisks, since otherwise it is |
393 |
at least two subdisks, since otherwise it is |
| 392 |
indistinguishable from a concatenated plex.</para> |
394 |
indistinguishable from a concatenated plex.</para> |
| 393 |
</listitem> |
395 |
</listitem> |
|
|
396 |
|
| 397 |
<listitem> |
| 398 |
<para>raid5 |
| 399 |
plexes implement redundancy with low volume overhead for the price |
| 400 |
of higher CPU load and relatively low write speed. As for striped |
| 401 |
plexes, subdisks involved must be the same size, and extending |
| 402 |
raid5 plex will need its complete reformatting. Minimal raid5 plex |
| 403 |
must contain at least 3 subdisks; due to performance reasons, 5 or |
| 404 |
more subdisks (all on different drives, of course) are |
| 405 |
recommended.</para> |
| 406 |
</listitem> |
| 394 |
</itemizedlist> |
407 |
</itemizedlist> |
| 395 |
|
408 |
|
| 396 |
<para><xref linkend="vinum-comparison"> summarizes the advantages |
409 |
<para><xref linkend="vinum-comparison"> summarizes the advantages |
|
Lines 427-432
Link Here
|
| 427 |
<entry>High performance in combination with highly concurrent |
440 |
<entry>High performance in combination with highly concurrent |
| 428 |
access</entry> |
441 |
access</entry> |
| 429 |
</row> |
442 |
</row> |
|
|
443 |
|
| 444 |
<row> |
| 445 |
<entry>radi5</entry> |
| 446 |
<entry>3</entry> |
| 447 |
<entry>no</entry> |
| 448 |
<entry>yes</entry> |
| 449 |
<entry>High read performance in combination with redundancy such |
| 450 |
as large data archives</entry> |
| 451 |
</row> |
| 430 |
</tbody> |
452 |
</tbody> |
| 431 |
</tgroup> |
453 |
</tgroup> |
| 432 |
</table> |
454 |
</table> |
|
Lines 708-713
Link Here
|
| 708 |
<graphic fileref="vinum/vinum-raid10-vol"> |
730 |
<graphic fileref="vinum/vinum-raid10-vol"> |
| 709 |
</figure> |
731 |
</figure> |
| 710 |
</para> |
732 |
</para> |
|
|
733 |
</sect2> |
| 734 |
|
| 735 |
<sect2> |
| 736 |
<title>Resilience and Performance: Hard Way</title> |
| 737 |
|
| 738 |
<para><anchor id="vinum-raid5">With sufficient hardware and CPU power, |
| 739 |
especially when most of disc activities are reads, it would be useful |
| 740 |
to make raid5 volume, which consumes only 1/n of disk volume for |
| 741 |
resilience instead of 1/2 for mirrored volumes, and still achieves |
| 742 |
great read performance. A typical configuration file might |
| 743 |
be:</para> |
| 744 |
|
| 745 |
<programlisting> |
| 746 |
volume raid5 |
| 747 |
plex org raid5 512k |
| 748 |
sd length 102480k drive a |
| 749 |
sd length 102480k drive b |
| 750 |
sd length 102480k drive c |
| 751 |
sd length 102480k drive d |
| 752 |
sd length 102480k drive e</programlisting> |
| 753 |
|
| 754 |
<para>Note we have single plex here because raid5 provides |
| 755 |
fault-tolerance itself.</para> |
| 756 |
|
| 711 |
</sect2> |
757 |
</sect2> |
| 712 |
</sect1> |
758 |
</sect1> |