1. Synology Technology
Alex Wang
May 1, 2008

2. Outline Hardware architecture Software architecture Performance
Competitive cost
Quality

3. Hardware Architecture

4. Hardware Specification
DS107
DS207+
DS407
DS508
CPU
Power PC 266MHz
ARM 500MHz
PowerPC 800MHz
RAM
64 MB
128MB
512MB
Flash
2 MB
4 MB
Disk 1 2 4 5
USB 3
AC Adapter
50W
70W
100W
250W

6. DS407 Board

7. Software Architecture

8. Software Architecture
1 source tree for multiple platform 5 CPU, 19 models
Only change boot loader, kernel, and toolchain
Sometimes build our own toolchain crosstool:
Chroot build process

9. Flash Layout 2 MB 4 MB Kernel Kernel 0xD0000, 832 KB 0x200000, 2MB
Hw config (0x10000)
Reserved 0x20000
Ramdisk
0x180000, 1.5MB
ppcboot (0x40000)
Ramdisk
0xD0000, 704KB
Hw config (0x10000)
Reserved 0x20000
FIS directory (0x10000)
FIS directory (0x10000)
uboot (0x40000)

10. Boot Procedure 6 3 7 2 5 1 8 8 4 Flash RAM Ramdisk init Ramdisk initrd
Kernel mounts memory disk
Flash
RAM 6
Ramdisk
init
Ramdisk 3
initrd
0x800000
0xFFE00000 7
Kernel
Kernel 2 5
Ramdisk
linuxrc.syno
0xFFC00000
0x80000
Copy kernel to RAM 1 8 8 4
Jump to kernel
Disk
/etc/rc
Boot loader
Ramdisk
/etc/rc

11. Boot Procedure

12. Software Architecture
Web Applications
Management UI
Network Service
Synology SDK Library
Linux Kernel, ,
Disk Driver
Network Driver
USB Driver
Synology HW driver

13. Performance

14. RAID 5 Read Performance Intel Celeron 3.2GHz Celeron M 1.5 GHz
ARM 500 MHz
ARM 500 MHz
ARM 500 MHz

15. RAID 5 Read Performance Intel Celeron 3.2GHz Celeron M 1.5 GHz
ARM 500 MHz
PowerPC 266 MHz
ARM 500 MHz

16. RAID 5 Write Performance

17. RAID 5 Read Performance
40% faster then original Linux kernel FTP download from 26 MB/s to 37 MB/s
1 year ahead to Linux kernel
How?

18. RAID 5 Read Performance At least 3 disks Allow 1 disk failure P 1 2 36 4 5 P 9 7 P 8 12 P 10 11

19. Stripe Cache (Used to check data consistency)
RAID 5 Read Performance
Read buffer
Memory copy
Stripe Cache (Used to check data consistency)
Memory copy P 1 2 3 6 4 5 P 9 7 P 8 12 P 10 11

20. Reduce Memory Copy Download file for (;;) {
cnt = read(file_fd, buf, sizeof(buf));
if (cnt <= 0) break;
for (len = cnt, bp = buf; len > 0;) {
cnt = write(sock_fd, bp, len);
if (cnt < 0) error;
len -= cnt;
bp+=cnt; }

21. Reduce Memory Copy User space daemon Disk read() Kernel memory copy
write()
Network
memory copy

22. Reduce Memory Copy cnt = sendfile(sock_fd, file_fd, offset, filesize);
User space daemon
Kernel
Disk
sendfile()
Network

23. Large Directory Handling
Windows uses case-insensitive
Unix/Linux is case-sensitive
How would Samba do to pretend it is case-insensitive?
Create/rename/delete/lookup

24. Large Directory Handling
Enumerate all files in the directory, convert file name to upper and do string compare!
What if there are more than 10,000 files in a directory?

25. Large Directory Handling
Modify EXT3 file system to be case-insensitive
Port EXT3 directory hash to 2.4 kernel open() 10,000 files from 2mins to 10 sec

26. Competitive Cost

27. Competitive Cost We are small company NAS is a small market
Big companies get lower price because they can share parts between different products
How to compete? Software!!

28. Competitive Cost – Flash size
We use 2 MB or 4 MB flash
Our competitor uses 16 MB flash (or 512 KB flash and bundle disk)
Don't bundle disk to avoid the risk of disk price decline
2 MB $3
4 MB $4
16 MB
$10

29. Competitive Cost – Flash size
Use 2.4 kernel smaller footprint, better performance, FTP 20% faster
Network installation The ramdisk in flash provides minimize function for installation only

30. Competitive Cost – Power Supply
A 1TB Disk needs 40W
PC server uses 350W power supply, noisy, large
We use 100W adapter for 4 disk model, quiet, small
100 W for 4 disk+PCB?
40W Adapter $4
50W adapter (1 disk)
$5.5
70W adapter (2 disks) $9
100W adapter (4 disks)
$22
250W (PC)
$28

31. Competitive Cost – Power Supply
Disk spin up 35 W
Disk access 14 W
Disk idle 12 W
Disk hibernation 0 W
PCB 7~12 W
Power up sequence

32. Competitive Cost – Power Supply

33. Competitive Cost – Power Supply
Power up sequence Software delay until disk ready, 40 seconds
How about hibernation?

34. Competitive Cost – Power Supply
Ask disk whether disk is hibernating before access it
When disk is hibernating and wake up the first disk
If other disks are waking up, put into queue to delay wake up
Extra command to ask status? Performance?

35. Quality

36. Quality - Reliability Mass stress 12pic x 14days for every release
MP - Stress memory for 24 hours
MP - Stress with disk for 24 hours
Production cost: 4 disks x 100 pics
Production capacity: 100 per day

37. Quality – Software Dainty
Continuous free firmware upgrade
Take care on small details
File created time
Unicode conversion
Extended attribute
RAID error handling

38. Quality – RAID Error Handling
Read error? P 1 2 B 6 4 5 P 9 7 P 8 12 P 10 11

39. Quality – RAID Error Handling
Rewrite to leverage disk bad sector mapping P 1 2 B 6 4 5 P 9 7 P 8 12 P 10 11 3

40. Q&A
Yes, we are hiring