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Raid and SSD

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May 9, 2010 12:58:48 PM

Does RAID 0 improve performance with SSD drives? Would three SSD in a RAID 0 be faster then two? Thank you for your help.

More about : raid ssd

a c 415 G Storage
May 9, 2010 4:46:43 PM

You'll get higher transfer rates, but the access times won't be any different.

There will probably be some speed improvement for tasks like booting and starting applications, but since the access times are the same you certainly won't see a 50% reduction in wait times with 2 drives.
a c 126 G Storage
May 9, 2010 5:48:55 PM

Here are some benchmarks done on FreeBSD (not Windows) on two Intel X25-V 40GB SSDs:

RAIDTEST (tests with sizes between 4KiB-128KiB; random pattern)
  1. RAIDTEST on /dev/stripe/str0 - testing random read/write performance
  2. concurrency performance in I/O's per sec. average
  3. 1 (4KiB) 1580 1585 1585 1583
  4. 1 (1MiB) 1577 1625 1702 1634
  5.  
  6. 2 (4KiB) 1902 1902 1900 1901
  7. 2 (1MiB) 2477 2493 2499 2489
  8.  
  9. 4 (4KiB) 2003 1994 2004 2000
  10. 4 (1MiB) 3209 3159 3192 3186
  11.  
  12. 16 (4KiB) 2021 2020 2019 2020
  13. 16 (1MiB) 4046 3949 4073 4022
  14.  
  15. 64 (4KiB) 2004 2007 2002 2004
  16. 64 (1MiB) 4178 4183 4184 4181
  17.  
  18. 128 (4KiB) 1999 2000 1995 1998
  19. 128 (1MiB) 4182 4181 4180 4181
  20.  
  21. 256 (4KiB) 2029 2034 2027 2030
  22. 256 (1MiB) 4298 4294 4297 4296



RAWIO (tests with fixed sizes 32KiB; random pattern)
  1. RAWIO benchmark (device: /dev/stripe/str0; chunksize: 32768; recordcount: 200000)
  2. arguments: rawio -I <workers> -p <workers> -h -R -F -s 12884901888 -c 32768 -n 200000 /dev/stripe/str0
  3.  
  4. Workers Random read Seq. read Random write Seq. write
  5. K/sec /sec K/sec /sec K/sec /sec K/sec /sec
  6.  
  7. [b]Single drive[/b]
  8. 1 191360.7 5840
  9. 2 258794.7 7898
  10. 4 274055.3 8364
  11. 8 276104.1 8426
  12. 16 274864.3 8388
  13. 32 271988.9 8300
  14. 64 271791.5 8294
  15. 128 271777.5 8294
  16. 256 271881.4 8297
  17.  
  18. [b]RAID0 - 4KiB stripesize[/b]
  19. 1 162690.8 4965
  20. 2 234824.0 7166
  21. 4 238313.2 7273
  22. 8 238627.2 7282
  23. 16 237883.2 7260
  24. 32 238015.2 7264
  25. 64 236909.9 7230
  26. 128 236493.1 7217
  27. 256 235869.8 7198
  28.  
  29. [b]RAID0 - 1MiB stripesize[/b]
  30. 1 185591.4 5664
  31. 2 323506.7 9873
  32. 4 446693.6 13632
  33. 8 507941.1 15501
  34. 16 532830.1 16261
  35. 32 540046.1 16481
  36. 64 542969.5 16570
  37. 128 543610.3 16590
  38. 256 545476.6 16647


So RAID0 can scale IOps quite nicely, also on SSDs. However, since the SSD is already so fast other areas will tend to bottleneck; like your CPU. The loss of TRIM is a setback; only on Linux and BSD can you have TRIM on SSDs in RAID.

SSDs in striping RAID would need perfect alignment or have very bad write amplification; using SSDs in RAID0 on Windows XP would be the worst-case with much lower performance than single-SSD without RAID. Windows 7 should be okay out of the box - stripesizes 128KiB and up.

Still - take a moment and decide whether it's worth the trouble.
May 9, 2010 7:35:16 PM

Really, it will be better for booting faster into the os (if its only the os) if you are using raid 0. Data transfers are not too common for use in an os. The more important thing is the access times. I mean there will be very little difference in raid 0 on an os other than when it is just booting up. Other than that YEA it will be "faster". You have to understand that the big thing about ssd's is their access times, not just their sustained reads. And the access times are unaffected when two ssds are put in raid 0. Even after i have already bought 2 ssds (compulsively) i am seriously debating whether to put them in raid 0 as intended. Mostly because of the lack of trim and because of the fact that they are already fast enough.
!