@ebo2002fr:
Does it worth increasing vm.kmem_size and vm.kmem_size_max ?
Not likely.
@ebo2002fr:
Do you think it is a hardware issue ?
Yes, your "hard drive" shouldn't be causing:
@ebo2002fr:
2013-07-18 13:27:05 crit routeur kern kernel ata2: hardware reset timeout
2013-07-18 13:27:04 crit routeur kern kernel ata2: port is not ready (timeout 10000ms)
2013-07-18 13:26:56 crit routeur kern kernel g_vfs_done():ad4s1a[WRITE(offset=192856064, length=16384)]error = 6
2013-07-18 13:26:56 crit routeur kern kernel g_vfs_done():ad4s1a[WRITE(offset=192856064, length=16384)]error = 6
2013-07-18 13:26:42 crit routeur kern kernel g_vfs_dkone():ad4s1a[WRITE(offset=6144000, length=2048)]error = 6
2013-07-18 13:26:42 crit routeur kern kernel ng_vfs_done():ad4s1a[WRITE(offset=65536, length=2048)]error = 6
2013-07-18 13:26:42 crit routeur kern kernel g_vfs_done():ad4s1a[WRITE(offset=199290880, length=2048)]uerror = 6
2013-07-18 13:26:42 crit routeur kern kernel ata2: hardware reset timeout
2013-07-18 13:26:42 crit routeur kern kernel ata2: port is not ready (timeout 10000ms) tfd = 00000080