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from: <a class="moz-txt-link-freetext" href="http://www.linux-mag.com/2001-11/guru_03.html">http://www.linux-mag.com/2001-11/guru_03.html</a><br>
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<p>Finally, let's consider creating a RAID 0+1 disk (mirrored striped
disks) in <i>Listing Three</i>.
This device is set up in the same way as any other RAID device. The
only difference is that the component disks are themselves RAID
devices. In this case, they will need to have been previously defined
as RAID 0 devices.</p>
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<p class="LISTING-TITLE"><font face="Arial,Helvetica,sans-serif"><i>Listing
Three: /etc/raidtab (RAID 0+1)</i></font></p>
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<pre>raiddev /dev/md2
raid-level 1
nr-raid-disks 2
persistent-superblock 1
device /dev/md0 # The component disks are RAID devices
raid-disk 0
device /dev/md1
raid-disk 1
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Hope that helps<br>
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-Pete<br>
<blockquote cite="mid20041008013208.428003C28078@basilica.la.naos.co.nz"
type="cite">
<pre wrap="">In message <a class="moz-txt-link-rfc2396E" href="mailto:20041007212712.17026.qmail@web12210.mail.yahoo.com"><20041007212712.17026.qmail@web12210.mail.yahoo.com></a>, Wood Brent writes:
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<pre wrap="">I want to maximise read performance using two drives under Linux software RAID.
Streaming large files (up to several Gb ea) & Postgres databases.
[....]
I don't know if Linux software RAID1 will read from both drives or not.
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<pre wrap=""><!---->
I believe it will.
<a class="moz-txt-link-freetext" href="http://www.tldp.org/HOWTO/Software-RAID-HOWTO-1.html#ss1.4">http://www.tldp.org/HOWTO/Software-RAID-HOWTO-1.html#ss1.4</a>
also implies that it will. Write performance on RAID-1 can be a little
so-so (due to the need to write to two disks, and worse if there are
limitations on overlapping I/O such as with IDE), but read performance
should be better than for a single drive particularly if they're
arranged so as to maximise the opportunity for overlapped I/O.
There are also some relatively inexpensive hardware RAID cards that are
well supported under Linux (3Ware, Adaptec, etc for IDE, plenty of
choices for SCSI).
Ewen
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