topic STrange behavior of LUNs in VA7410 in Operating System - HP-UX

STrange behavior of LUNs in VA7410

Igor I. Shulz — Tue, 01 Mar 2005 10:12:34 GMT

I have the next LUNs, created in VA7410 - /dev/dsk/c8t0d0
/dev/dsk/c9t0d1
/dev/dsk/c8t0d6
/dev/dsk/c9t0d7
/dev/dsk/c8t1d0
/dev/dsk/c9t1d1
/dev/dsk/c9t0d0
/dev/dsk/c8t0d1
/dev/dsk/c9t0d6
/dev/dsk/c8t0d7
/dev/dsk/c9t1d0
/dev/dsk/c8t1d1
There is VG, created on them:
VG Name /dev/vg_raw
VG Write Access read/write
VG Status available
Max LV 50
Cur LV 30
Open LV 30
Max PV 16
Cur PV 6
Act PV 6
Max PE per PV 14080
VGDA 12
PE Size (Mbytes) 4
Total PE 84462
Alloc PE 70262
Free PE 14200
Total PVG 0
Total Spare PVs 0
Total Spare PVs in use 0
...
--- Physical volumes ---
PV Name /dev/dsk/c8t0d0
PV Name /dev/dsk/c9t0d0 Alternate Link
..........
PV Name /dev/dsk/c8t1d0
PV Name /dev/dsk/c9t1d0 Alternate Link
PV Status available
Total PE 14077
Free PE 7100
Autoswitch On

PV Name /dev/dsk/c9t1d1
PV Name /dev/dsk/c8t1d1 Alternate Link
PV Status available
Total PE 14077
Free PE 7100
Autoswitch On

During any r/w operations on volumes of this VG I see even (equal) distribution of r+w/s and blks/s values between LUNs that keep this VG, (shown by sar). But values %busy and avserv are different:

device %busy avque r+w/s blks/s avwait avserv
17:00:33 c8t1d0 70.10 1.04 597 4757 5.27 2.13
c9t1d1 97.01 1.11 578 4601 5.40 5.46
17:00:36 c8t1d0 64.88 0.66 886 7080 5.16 1.25
c9t1d1 99.67 0.74 882 7046 5.48 4.21
17:00:39 c8t1d0 51.16 1.49 428 3409 5.23 1.90
c9t1d1 98.67 1.57 441 3518 6.14 7.71

All volumes on thin VG were created with stripe over 2 LUNs. Why %busy and avserv are very different on neighbor LUNs, though number of blocks per secund are almost the same? Is it a problem?

Thank you

PS: all neighbor LUNs has equal size.

Re: STrange behavior of LUNs in VA7410

Bonnyjose_1 — Wed, 02 Mar 2005 09:57:45 GMT

Is the number of disks in each Redundancy Group are same? Also is both RGs of VA are equally utilised?
-Bonny-

Re: STrange behavior of LUNs in VA7410

Igor I. Shulz — Wed, 02 Mar 2005 10:52:58 GMT

Well, we have 24 and 21 disks in RGs. This could be source of that behavior, but it seems that it isn't.

device %busy avque r+w/s blks/s avwait avserv
c8t1d0 43.67 1.40 1422 10951 5.21 0.66
c9t1d1 89.33 1.63 1372 10934 6.18 2.60

24 and 21 are different on 13-15%, but %busy in this case is different by twice (43 and 89).

In commandView IO-rates (total IO-rate Graph) for both these LUNs are almost the same.

I dont know how to check utilization by RG.

It seems that sar is simply not quite accurate tool in this case.

Re: STrange behavior of LUNs in VA7410

Tim D Fulford — Wed, 02 Mar 2005 11:05:58 GMT

how have you striped over the 6 Luns & 6 alternate paths. remember the va7410 does internal striping, but the OS does not know about this, so it is perfectly possible for more of your LVs to be on c8t1d0.

The other thing (assuming the striping is even) is that c9t1d0 is MUCH slower than c8t1d0 (by a factor of 3-4). My guess is that RG2 (say) has had a disk failure and data is
o converting to RAID5DP,
o "make space" command is running,
o there is alot of data in RAID5DP.

Any of the above will hammer performance for that RG. First stop would be to run
armdsp -a
From this you may also look into running
armlog ...
prnlog ...

regards

Tim