We actually hit similar issues with LSI, but within workload not scrub, result 
is same but it seems to choke on writes rather than reads with suboptimal 
performance.
http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6891413

Anyway, we haven't experienced this _at all_ with RE3-version of Western 
Digital disks..
Issues seem to pop up with 750GB seagate and 1TB WD black-series, so far 2TB 
green WDs seem unaffected too, so might it be related to disks firmware due how 
they chat with LSI?

Also, we noticed more severe (even RE3 and 2TBWD green) timeouts if disks are 
not forced into SATA1-mode, I believe this is known issue with newer 2TB disks 
and some other disk controllers and may be caused by bad cabling or 
connectivity.

We have never witnessed this behaviour with SAS (fujitsu,ibm..) also. All this 
happens with snv 118,122,123 and 125.

Yours
Markus Kovero

________________________________________
Lähettäjä: zfs-discuss-boun...@opensolaris.org 
[zfs-discuss-boun...@opensolaris.org] käyttäjän Adam Cheal 
[ach...@pnimedia.com] puolesta
Lähetetty: 24. lokakuuta 2009 12:49
Vastaanottaja: zfs-discuss@opensolaris.org
Aihe: Re: [zfs-discuss] SNV_125 MPT warning in logfile

The iostat I posted previously was from a system we had already tuned the 
zfs:zfs_vdev_max_pending depth down to 10 (as visible by the max of about 10 in 
actv per disk).

I reset this value in /etc/system to 7, rebooted, and started a scrub. iostat 
output showed busier disks (%b is higher, which seemed odd) but a cap of about 
7 queue items per disk, proving the tuning was effective. iostat at a 
high-water mark during the test looked like this:

                    extended device statistics
    r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0 c8
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0 c8t0d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0 c8t1d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0 c8t2d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0 c8t3d0
 8344.5    0.0 359640.4    0.0  0.1 300.5    0.0   36.0   0 4362 c9
  190.0    0.0 6800.4    0.0  0.0  6.6    0.0   34.8   0  99 c9t8d0
  185.0    0.0 6917.1    0.0  0.0  6.1    0.0   32.9   0  94 c9t9d0
  187.0    0.0 6640.9    0.0  0.0  6.5    0.0   34.6   0  98 c9t10d0
  186.5    0.0 6543.4    0.0  0.0  7.0    0.0   37.5   0 100 c9t11d0
  180.5    0.0 7203.1    0.0  0.0  6.7    0.0   37.2   0 100 c9t12d0
  195.5    0.0 7352.4    0.0  0.0  7.0    0.0   35.8   0 100 c9t13d0
  188.0    0.0 6884.9    0.0  0.0  6.6    0.0   35.2   0  99 c9t14d0
  204.0    0.0 6990.1    0.0  0.0  7.0    0.0   34.3   0 100 c9t15d0
  199.0    0.0 7336.7    0.0  0.0  7.0    0.0   35.2   0 100 c9t16d0
  180.5    0.0 6837.9    0.0  0.0  7.0    0.0   38.8   0 100 c9t17d0
  198.0    0.0 7668.9    0.0  0.0  7.0    0.0   35.3   0 100 c9t18d0
  203.0    0.0 7983.2    0.0  0.0  7.0    0.0   34.5   0 100 c9t19d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0 c9t20d0
  195.5    0.0 7096.4    0.0  0.0  6.7    0.0   34.1   0  98 c9t21d0
  189.5    0.0 7757.2    0.0  0.0  6.4    0.0   33.9   0  97 c9t22d0
  195.5    0.0 7645.9    0.0  0.0  6.6    0.0   33.8   0  99 c9t23d0
  194.5    0.0 7925.9    0.0  0.0  7.0    0.0   36.0   0 100 c9t24d0
  188.5    0.0 6725.6    0.0  0.0  6.2    0.0   32.8   0  94 c9t25d0
  188.5    0.0 7199.6    0.0  0.0  6.5    0.0   34.6   0  98 c9t26d0
  196.0    0.0 6666.9    0.0  0.0  6.3    0.0   32.1   0  95 c9t27d0
  193.5    0.0 7455.4    0.0  0.0  6.2    0.0   32.0   0  95 c9t28d0
  189.0    0.0 7400.9    0.0  0.0  6.3    0.0   33.2   0  96 c9t29d0
  182.5    0.0 9397.0    0.0  0.0  7.0    0.0   38.3   0 100 c9t30d0
  192.5    0.0 9179.5    0.0  0.0  7.0    0.0   36.3   0 100 c9t31d0
  189.5    0.0 9431.8    0.0  0.0  7.0    0.0   36.9   0 100 c9t32d0
  187.5    0.0 9082.0    0.0  0.0  7.0    0.0   37.3   0 100 c9t33d0
  188.5    0.0 9368.8    0.0  0.0  7.0    0.0   37.1   0 100 c9t34d0
  180.5    0.0 9332.8    0.0  0.0  7.0    0.0   38.8   0 100 c9t35d0
  183.0    0.0 9690.3    0.0  0.0  7.0    0.0   38.2   0 100 c9t36d0
  186.0    0.0 9193.8    0.0  0.0  7.0    0.0   37.6   0 100 c9t37d0
  180.5    0.0 8233.4    0.0  0.0  7.0    0.0   38.8   0 100 c9t38d0
  175.5    0.0 9085.2    0.0  0.0  7.0    0.0   39.9   0 100 c9t39d0
  177.0    0.0 9340.0    0.0  0.0  7.0    0.0   39.5   0 100 c9t40d0
  175.5    0.0 8831.0    0.0  0.0  7.0    0.0   39.9   0 100 c9t41d0
  190.5    0.0 9177.8    0.0  0.0  7.0    0.0   36.7   0 100 c9t42d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0 c9t43d0
  196.0    0.0 9180.5    0.0  0.0  7.0    0.0   35.7   0 100 c9t44d0
  193.5    0.0 9496.8    0.0  0.0  7.0    0.0   36.2   0 100 c9t45d0
  187.0    0.0 8699.5    0.0  0.0  7.0    0.0   37.4   0 100 c9t46d0
  198.5    0.0 9277.0    0.0  0.0  7.0    0.0   35.2   0 100 c9t47d0
  185.5    0.0 9778.3    0.0  0.0  7.0    0.0   37.7   0 100 c9t48d0
  192.0    0.0 8384.2    0.0  0.0  7.0    0.0   36.4   0 100 c9t49d0
  198.5    0.0 8864.7    0.0  0.0  7.0    0.0   35.2   0 100 c9t50d0
  192.0    0.0 9369.8    0.0  0.0  7.0    0.0   36.4   0 100 c9t51d0
  182.5    0.0 8825.7    0.0  0.0  7.0    0.0   38.3   0 100 c9t52d0
  202.0    0.0 7387.9    0.0  0.0  7.0    0.0   34.6   0 100 c9t55d0

...and sure enough about 20 minutes into it I get this (bus reset?):

scsi: [ID 107833 kern.warning] WARNING: 
/p...@0,0/pci8086,6...@4/pci1000,3...@0/s...@34,0 (sd49):
       incomplete read- retrying
scsi: [ID 107833 kern.warning] WARNING: 
/p...@0,0/pci8086,6...@4/pci1000,3...@0/s...@21,0 (sd30):
       incomplete read- retrying
scsi: [ID 107833 kern.warning] WARNING: 
/p...@0,0/pci8086,6...@4/pci1000,3...@0/s...@1e,0 (sd27):
       incomplete read- retrying
scsi: [ID 365881 kern.info] /p...@0,0/pci8086,6...@4/pci1000,3...@0 (mpt0):
       Rev. 8 LSI, Inc. 1068E found.
scsi: [ID 365881 kern.info] /p...@0,0/pci8086,6...@4/pci1000,3...@0 (mpt0):
       mpt0 supports power management.
scsi: [ID 365881 kern.info] /p...@0,0/pci8086,6...@4/pci1000,3...@0 (mpt0):
       mpt0: IOC Operational.

During the "bus reset", iostat output looked like this:

                            extended device statistics       ---- errors ---
    r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b s/w h/w trn tot 
device
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 c8
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c8t0d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c8t1d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c8t2d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c8t3d0
    0.0    0.0    0.0    0.0  0.0 88.0    0.0    0.0   0 2200   0   3   0   3 c9
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t8d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t9d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t10d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t11d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t12d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t13d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t14d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t15d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t16d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t17d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t18d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t19d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t20d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t21d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t22d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t23d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t24d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t25d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t26d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t27d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t28d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t29d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   1   0   1 
c9t30d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t31d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t32d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   1   0   1 
c9t33d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t34d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t35d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t36d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t37d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t38d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t39d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t40d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t41d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t42d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t43d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t44d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t45d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t46d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t47d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t48d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t49d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t50d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   0   0   0 
c9t51d0
    0.0    0.0    0.0    0.0  0.0  4.0    0.0    0.0   0 100   0   1   0   1 
c9t52d0
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0   0   0   0   0 
c9t55d0

During our previous testing, we had tried even setting this max_pending value 
down to 1, but we still hit the problem (albeit it took a little longer to hit 
it) and I couldn't find anything else I could set to throttle IO to the disk, 
hence the frustration.

If you hadn't seen this output, would you say that 7 was a "reasonable" value 
for that max_pending queue for our architecture and should give the LSI 
controller in this situation enough breathing room to operate? If so, I 
*should* be able to scrub the disks successfully (ZFS isn't to blame) and 
therefore have to point the finger at the mpt-driver/LSI-firmware/disk-firmware 
instead.
--
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