Embora o iostat e o kstat sejam úteis, como você tem o Solaris com o ZFS (10 ou mais), aproveite a Arquitetura de Gerenciamento de Falhas (FMA), que está ligada ao zfs e a muitas outras partes do o SO.
Observe a saída de 'fmdump' para ver se houve alguma falha. Como exemplo (com saída repetida elidida):
$ fmdump -u af2a7c20-05f9-ef95-b016-fcfa812c4f81
TIME UUID SUNW-MSG-ID EVENT
Aug 15 15:48:16.3800 af2a7c20-05f9-ef95-b016-fcfa812c4f81 ZFS-8000-LR Diagnosed
Aug 15 15:58:16.2179 af2a7c20-05f9-ef95-b016-fcfa812c4f81 FMD-8000-9L Isolated
Sep 01 10:11:17.6591 af2a7c20-05f9-ef95-b016-fcfa812c4f81 FMD-8000-9L Isolated
Oct 09 21:45:57.0520 af2a7c20-05f9-ef95-b016-fcfa812c4f81 FMD-8000-9L Isolated
Oct 24 17:21:48.9799 af2a7c20-05f9-ef95-b016-fcfa812c4f81 FMD-8000-9L Isolated
Nov 02 12:41:30.4093 af2a7c20-05f9-ef95-b016-fcfa812c4f81 FMD-8000-4M Repaired
Nov 02 12:41:30.4169 af2a7c20-05f9-ef95-b016-fcfa812c4f81 FMD-8000-6U Resolved
e com um pouco mais de detalhe:
$ fmdump -v -u af2a7c20-05f9-ef95-b016-fcfa812c4f81
TIME UUID SUNW-MSG-ID EVENT
Aug 15 15:48:16.3800 af2a7c20-05f9-ef95-b016-fcfa812c4f81 ZFS-8000-LR Diagnosed
100% fault.fs.zfs.open_failed
Problem in: zfs://pool=6e954c71737e8931/vdev=b0b1eb6df8896769/pool_name=soundandvision/vdev_name=id1,sd@SATA_____Hitachi_HDS72101______JPS911N11TBURL/a
Affects: zfs://pool=6e954c71737e8931/vdev=b0b1eb6df8896769/pool_name=soundandvision/vdev_name=id1,sd@SATA_____Hitachi_HDS72101______JPS911N11TBURL/a
FRU: zfs://pool=6e954c71737e8931/vdev=b0b1eb6df8896769/pool_name=soundandvision/vdev_name=id1,sd@SATA_____Hitachi_HDS72101______JPS911N11TBURL/a
FRU Location: -
Observe que, se você tiver seus discos dentro de um jbod com informações de localização do SES, ou se tiver uma matriz suportada, poderá ver a localização do disco em questão, assim:
$ fmdump -v -u 80db2054-3954-49bf-b705-8820542679fc
TIME UUID SUNW-MSG-ID EVENT
Nov 09 08:09:10.0909 80db2054-3954-49bf-b705-8820542679fc DISK-8000-6R Diagnosed
100% fault.io.scsi.disk.tran.unstable.leaf
Problem in: hc://:chassis-mfg=Oracle-Corporation:chassis-name=ORACLE-DE2-24C:chassis-part=31883801+1+1:chassis-serial=1330FMT006:fru-mfg=HITACHI:fru-name=H7230AS60SUN3.0T:fru-serial=001229RSEGSD--------YHKSEGSD:fru-part=HITACHI-H7230AS60SUN3.0T:fru-revision=A142:devid=id1,sd@n5000cca01ad3b688/ses-enclosure=0/bay=16/disk=0
Affects: dev:///:devid=id1,sd@n5000cca01ad3b688//scsi_vhci/disk@g5000cca01ad3b688
FRU: hc://:chassis-mfg=Oracle-Corporation:chassis-name=ORACLE-DE2-24C:chassis-part=31883801+1+1:chassis-serial=1330FMT006:fru-mfg=HITACHI:fru-name=H7230AS60SUN3.0T:fru-serial=001229RSEGSD--------YHKSEGSD:fru-part=HITACHI-H7230AS60SUN3.0T:fru-revision=A142:devid=id1,sd@n5000cca01ad3b688/ses-enclosure=0/bay=16/disk=0
FRU Location: /ORACLE-DE2-24C.1330FMT006/Disk-16