Presented this talk in FudCon 2015 event.

1. Storage Issue Troubleshooting
From OS side
Ajit Subhash Mote
Senior Technical Support Engineer,redhat
27 Jun 2015, Fudcon,Pune

2. What this session is all about !
 What is Mean By “Storage troubleshooting”

Different storage component

Device Mapper

Device Mapper Multipath

Logical Volume Manager

Storage Performance

3. Storage troubleshooting

4. Components which we call
Storage
 Kernel Space components
➢
SCSI Subsystem :
upper layer (sd,st ...etc)
middle layer (scsi_mod)
lower layer (qla2xxx, lpfc ...etc )
➢
Device mapper (dm_mod, dm_mirror,
dm_log ...etc) modules
➢
Multipath driver (dm_multipath)
➢
vmcore crash analysis

5. Components which we call
Storage
 User Space components
➢
Logical Volume Manager (LVM) 2
➢
Device Mapper Multipath
➢
Tape Devices
➢
RAID (dmraid, mdraid)
➢
iSCSI
➢
Storage Area Network (SAN)
➢
Filesystems going read only

6. Components which we call
Storage
 Performance tuning
➢
High await
➢
System/Application is slow
➢
Other server is more faster

7. Storage Area Network (SAN)

8. Device Mapper

Device mapper is kernel driver (dm_mod.ko) that provides
a modular generic framework for volume management.
●
This framework help or used to construct new block
devices from existing block devices according to a table of
rules.
●
Applications that need to create new mapped devices
talk to the device mapper via the libdevmapper.so shared
library, which in turn issues ioctls to the
/dev/mapper/control device node.
●
Applications should manage metadata independently, in
kernel or userspace, and use the Device Mapper API to set
up the virtual device.

9. Device Mapper

10. Device Mapper multipath

11. Logical Volume Manager (LVM)

Widely­used technique for deploying logical rather than physical
storage.

Volume Management creates a layer of abstraction (logical
volumes) over the block devices.

LVM is based on the Device­Mapper.

LVM is implemented in userspace and not in kernel space.

LVM keeps a metadata header at the start of every physical
volume, each of which is uniquely identified by a UUID.

pvcreate command places the physical volume label in the 2nd
512­byte sector.

12. Logical Volume Manager (LVM)

Directories
➢
/etc/lvm default lvm directory location
➢
/etc/lvm/backup where the automatic backups go
➢
/etc/lvm/cache persistent filter cache
➢
/etc/lvm/archive archives go after a volume group change
➢
/var/lock/lvm lock files to prevent metadata corruption

Files
➢
/etc/lvm/lvm.conf main lvm configuration file
➢
/etc/lvm/cache/.cache cached valid devices list

13. Storage Performance

iostat

vmstat

mpstat

top

blktrace

14. Thank You