zfs, a directory that used to hold lot of files and listing pause

[Eugene M. Zheganin]

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.