1. MATSUMOTO Hitoshi matsumotohitosh@jp.fujitsu.com
SCSI support on Xen
MATSUMOTO Hitoshi
Fujitsu Ltd.

2. personal use available business use reliability and availability
Why SCSI?
Current Xen status
personal use available
business use reliability and availability
are required
reliability backup with SCSI function
availability SCSI control

3. business use (Large system)
The major backup media is Tape device. BACKUP is indispensable to large system. The backup software uses SCSI command to control tape drive and media changer.
The data base software for large system issues SCSI command directly (SCSI pass through) to disk.
LAN
server
server
DB server
Backup server
SCSI command
SCSI command
SCSI driver
SCSI driver FC FC FC FC FC FC FC FC FC FC
Disk
Tape

4. Current status of SCSI support on Xen
SCSI frontend/backend drivers were proposed by Fujita-san at the Xen Summit 2006.
Xen SCSI driver tgt model
Key word ;
- SCSI protocol processing in user space
- tgt: framework for storage target drivers

5. SCSI driver tgt model
Able to create, debug and maintain in user space → Free from kernel
Enable access: raw partitions, regular files, LVM, files over network, etc.
Supported disk device.
sd/st/sr/sg
scsi
HBA driver
Hypervisor
SCSI device
tgt core
user space
kernel space
Host (Dom 0)
Guest
SCSI disk
emulation
tgt daemon
SCSI back driver
SCSI front driver

6. SCSI driver tgt model
kernel space(tgt core)→user space(tgt daemon)→kernel space(HBA driver) makes overhead for performance．
Other devices (tape, media changer, etc) are not supported.
sd/st/sr/sg
scsi
HBA driver
Hypervisor
SCSI device
tgt core
user space
kernel space
Host (Dom 0)
Guest
SCSI disk
emulation
tgt daemon
SCSI back driver
SCSI front driver

7. IOPS VBD vs SCSI driver (tgt model)
version: based on Xen 3.0.4
CPU: host vcpu=1, guest vcpu=1
Memory: host=737MB, guest=256MB
Tool: iozone
Disk access: random, O_DIRECT
Block size: 8KB
SCSI
VBD
Read
54.0
220.4
Write
89.4
118.3
We need performance!

8. SCSI passthrough driver model
This architecture is similar to the current Xen driver(VBD) model.
Backend driver works in kernel.( SCSI is processed in kernel space)
Host (Dom 0)
Guest
sd/st/sr/sg
kernel space
scsi
SCSI passthrough
HBA driver
SCSI back driver
SCSI front driver
Hypervisor
SCSI device
This SCSI passtrough driver supports
disk, tape drive and media changer
FC-SCSI

9. SCSI driver passthrough model structure
Host (Dom0)
File I/O
guest
VFS
VFS
file_operations
Device
Device
ext3
ext3
page
BufferCashe
BufferCashe
SCSI backend driver
bio
scsi_cmnd
Block device
Block device
request
request
SCSI driver
SCSI driver
scsi_cmnd
SCSI frontend driver
HBA driver
scsi_cmnd
HYPERVISOR
disk

10. more reliability and performance
Redundancy and Load balance multi path support
application
application
sd/st/sg
scsi_mod
sd/st/sg
scsi_mod
HBA native
driver
HBA native
driver
HBA card
HBA card
HBA card
disk
disk

11. fail over: alternate path retry load balance: multi access path
multi path driver
fail over: alternate path retry
load balance: multi access path
application
sd/st/sg
scsi_mod
multi path driver
HBA card
disk
application
sd/st/sg
scsi_mod
multi path driver
HBA card
HBA card
disk
fail over
load balance

12. SCSI driver passthrough model structure 2
Host (Dom0)
File I/O
guest
VFS
VFS
file_operations
Device
Device
ext3
ext3
page
BufferCashe
BufferCashe
SCSI backend driver
bio
scsi_cmnd
Block device
Block device
request
request
SCSI driver
SCSI driver
scsi_cmnd
multi path driver
SCSI frontend driver
HBA driver
scsi_cmnd
HYPERVISOR
disk

13. SCSI driver support
Enable to issue SCSI command directly from each guest．
Each FC HBA card is assigned to one guest.
host
guest 1
guest 2
Host OS
I/O operation
I/O operation
SCSI backend
driver
SCSI backend
driver
guest OS
guest OS
SCSI frontend
driver
SCSI frontend
driver
FC(SCSI) native
driver
FC(SCSI) native
driver
Hypervisor
文責:山本哲
FC HBA card
FC HBA card
SAN

14. NPIV (N-Port Identifier Virtualization)
Virtual HBAs hosted by a physical HBA, unique SAN identify for each virtual HBAs.
HBA driver
HBA driver
HBA card
HBA card
HBA card
HBA card
SAN
SAN
NPIV not supported
NPIV supported

15. SCSI driver(NPIV) support
Enable to issue SCSI command directly from each guest．
host
guest 1
guest 2
Host OS
I/O operation
I/O operation
SCSI backend
driver
SCSI backend
driver
guest OS
guest OS
SCSI frontend
driver
SCSI frontend
driver
FC(SCSI) native
driver with NPIV
Hypervisor
文責:山本哲
FC HBA card with NPIV
SAN

16. I/O server domain support
Host domain
I/O server domain
Guest 1
Guest 2
host OS
Driver OS
I/O operation
I/O operation
guest OS
guest OS
VBD backend driver
VBD
frontend driver
VBD
frontend driver
disk native driver
Hypervisor
HBA card
HBA card

17. VT-d support Host domain Guest 1 Guest 2 Hypervisor FC HBA card
Host OS
I/O operation
I/O opetation
guest OS
guest OS
FC(SCSI)
native driver
FC(SCSI)
native driver
Hypervisor
FC HBA card
FC HBA card

18. road map
2007/2Q 3Q 4Q
FC-SCSI
NPIV
submit code
submit code