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Date: Sat, 21 Oct 2017 16:08:42 +0000 (UTC)
From: matthew patton <pattonme@yahoo.com>
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Subject: Re: [linux-lvm] cache on SSD makes system unresponsive
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To: Mike Snitzer <snitzer@redhat.com>, Oleg Cherkasov <o1e9@member.fsf.org>, LVM general discussion and development <linux-lvm@redhat.com>
Cc: ejt@redhat.com

>  But if it's something that only exhibits in writeback mode rather than writethrough, then I'd guess it's to do with the
> list of writeback work that the policy builds.  So check

OP is being coy about the DD command but I saw it mentioned off-hand earlier.

dd if=/250GB_file/on_LVM/H800_vdev of=/dev/null

It's a pure, streaming read. LVM cache should be doing absolutely nothing.