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[solved] Playing with mdadm
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Tux12Fun
Tux's lil' helper
Tux's lil' helper


Joined: 16 Aug 2007
Posts: 149

PostPosted: Wed Aug 15, 2012 12:14 pm    Post subject: [solved] Playing with mdadm Reply with quote

Hello,

I build the following setup, only for playing, but i haven't expected that this would be so slow.

Does anybody know how its so slow.

Setup:

DISK1 (USB - HDD)
=========================
= f1, f2, f3, f4, f5, f6, f7, f8, f9, f10 =
=========================

DISK2 (USB - HDD)
================================
= f11, f12, f13, f14, f15, f16, f17, f18, f19, f20 =
================================

Every File (f1-f20) is bound to one loop device (loop1-20)

now i build my raid (only for space/none security) like this. (Files have different size so i use linear)
mdadm --build --auto=part --verbose /dev/md0 --level linear -c 2048 -n 20 /dev/loop1 /dev/loop11 /dev/loop2 /dev/loop12 /dev/loop3 /dev/loop13 ...

Now I expected to write with the throughput of at least one disk (26mb/s) but if i write with dd i get only 6mb/s. Writing to a loop device is working with about 23mb/s


Last edited by Tux12Fun on Wed Aug 15, 2012 11:26 pm; edited 1 time in total
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eccerr0r
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Joined: 01 Jul 2004
Posts: 3899
Location: USA

PostPosted: Wed Aug 15, 2012 4:08 pm    Post subject: Reply with quote

What are you trying to do here?
There are multiple layers of filesystem munging translation here, that's one possible reason; also the possibility of fragmentation hurts this...
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NeddySeagoon
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Joined: 05 Jul 2003
Posts: 31907
Location: 56N 3W

PostPosted: Wed Aug 15, 2012 4:55 pm    Post subject: Reply with quote

Tux12Fun,

... and all this fun on USB, where there is no DMA for HDDs.

If you want to play with mdadm on USB, use real partitions and non journalling filesystems.
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