dm-cache caching network volume

["Étienne BERSAC" <etienne.bersac@nonstop.fr>]

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Hi,

I'm testing dm-cache for using a local SSD as a cache for a network
volume. My goal is to test dm-cache behaviour when network is down.

The device is shared through iSCSI. The first test is filling a huge
file with dd from /dev/zero. So, this is sequential access. While dd is
running, i remove the tun iface from the bridge on the host. iSCSI
properly detects the network failure.

I expected dm-cache to continue filling dirty blocks, even if the
network device is blocking. But it doesn't. The status shows that dirty
blocks count stays the same. dd is blocking.

I'm wondering if there is some cache desactivation due to
sequential_threshold. But increasing sequential_threshold did not help.
Where does dm-cache blocks ?

Is it possible to have dm-cache "bufferize" blocks for network
failures ?

Regards,
-- 
Étienne BERSAC <etienne.bersac@nonstop.fr>
NON STOP Systems

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