I would like how may I improve the situation of my lustre cluster.

I have 1 MDS and 1 OSS with 20 OST defined.

Each OST is a 8x Disks RAIDZ2.

A single process write performance is around 800MB/sec

anyway if I force direct I/O, for example using oflag=direct in dd, the write performance drop as low as 8MB/sec

with 1MB block size. And each write it's about 120ms latency.

I used these ZFS settings

options zfs zfs_prefetch_disable=1
options zfs zfs_txg_history=120
options zfs metaslab_debug_unload=1

i am quite worried for the low performance.

Any hints or suggestions that may help me to improve the situation ?

thank you


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