Hi,

I got a wired write performance and need your help.

One day, the write performance of zfs degrade.
The write performance decrease from 60MB/s to about 6MB/s in sequence write.

Command:
date;dd if=/dev/zero of=block bs=1024*128 count=10000;date

The hardware configuration is 1 Dell MD3000 and 1 MD1000 with 30 disks.
The OS is Solaris 10U8, zpool version 15 and zfs version 4.

I run Dtrace to trace the write performance:

fbt:zfs:zfs_write:entry
{
        self->ts = timestamp;
}


fbt:zfs:zfs_write:return
/self->ts/
{
        @time = quantize(timestamp-self->ts);
        self->ts = 0;
}

It shows
           value  ------------- Distribution ------------- count
            8192 |                                         0
           16384 |                                         16
           32768 |@@@@@@@@@@@@@@@@@@@@@@@@                 3270
           65536 |@@@@@@@                                  898
          131072 |@@@@@@@                                  985
          262144 |                                         33
          524288 |                                         1
         1048576 |                                         1
         2097152 |                                         3
         4194304 |                                         0
         8388608 |@                                        180
        16777216 |                                         33
        33554432 |                                         0
        67108864 |                                         0
       134217728 |                                         0
       268435456 |                                         1
       536870912 |                                         1
      1073741824 |                                         2
      2147483648 |                                         0
      4294967296 |                                         0
      8589934592 |                                         0
     17179869184 |                                         2
     34359738368 |                                         3
     68719476736 |                                         0

Compare to a working well storage(1 MD3000), the max write time of zfs_write is 4294967296, it is about 10 times faster.

Any suggestions?

Thanks
Ding

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