Hi.

On 20.10.2016 18:54, Nicolas Gilles wrote:
Looks like it's not taking up any processing time, so my guess is
the lag probably comes from stalled I/O ... bad disk?
Well, I cannot rule this out completely, but first time I've seen this lag on this particular server about two months ago, and I guess two months is enough time for zfs on a redundant pool to ger errors, but as you can see:

]# zpool status
  pool: zroot
 state: ONLINE
status: One or more devices are configured to use a non-native block size.
        Expect reduced performance.
action: Replace affected devices with devices that support the
        configured block size, or migrate data to a properly configured
        pool.
  scan: resilvered 5.74G in 0h31m with 0 errors on Wed Jun  8 11:54:14 2016
config:

        NAME            STATE     READ WRITE CKSUM
        zroot           ONLINE       0     0     0
          mirror-0      ONLINE       0     0     0
gpt/zroot0 ONLINE 0 0 0 block size: 512B configured, 4096B native
            gpt/zroot1  ONLINE       0     0     0

errors: No known data errors

there's none. Yup, disks have different sector size, but this issue happened with one particular directory, not all of them. So I guess this is irrelevant.

Does a second "ls" immediately returned (ie. metadata has been
cached) ?

Nope. Although the lag varies slightly:

        4.79s real              0.00s user              0.02s sys
        5.51s real              0.00s user              0.02s sys
        4.78s real              0.00s user              0.02s sys
        6.88s real              0.00s user              0.02s sys

Thanks.
Eugene.

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