Sql-server – SQL Disk Setup Advice – TempDB, Log DB, Data file placement question

disk-structuressansql-server-2008

We have a very active database server with a ecclectic collection of applications running on it. Two of the busiest are a Laserfiche database that does document scanning and workflow processing all day long (average of around 2800 batch requests / second) and a blackberry server app that routes emails. There are also about 25 other small application databases.

We're a govt agency so we were only given the budget for a single DB server license.

Recently we were given a SAN to address disk contention issues.

So currently we have the TempDB running on it's own disk (raid 1 mirror pair), and we've moved the transaction logs and data files onto the SAN. The transaction logs were put in one logical location and the data files in another. Physically it's the same array but it's an array made up of 14 total spindles (disks) in a raid 1+0 configuration.

A pretty beefy SAN – and things are running much better. Queue lengths cut in half.

Just today we were also given another option. We could also have a 4 disk array if we needed it currently on the file server. I know having MDF and LDF on two separate arrays is generally recommended but the only way to do that in our situation would be to move either data or transaction logs off the SAN onto the 4 disk array configured as Raid 5. Keep in mind they are currently in separate logical volumes but sharing the same physical array.

Shooting from the hip I feel like having the MDFs and LDFs together on a 14 spindle raid 1+0 array is probably as good as having them separate with one on a 4 spindle raid 5 array. But, I wouldn't be here asking if I was a disk logic expert. Both options are using basically identical 15k SAS disks – i.e. each spindle is basically indentical.

So, in essence the question is. Is having MDF / LDF on a single 14 spindle array configured as raid 1+0 going to be improved by any significant margin (or at all) by moving either data or log to it's own 4 spindle raid 5 array?

Thoughts?

UPDATED INFO:

I will also note that currently average queue length on the Log volume stays pretty consistently around 0.55. The average queue length on Data volume is rarely more than 0.01 (usually 0.00)

sys.dm_io_virtual_file_stats QUERY RESULT:

<table>
 <tr>
  <td>database
  id</td>
  <td>Volume</td>
  <td>io_stall_read_ms</td>
  <td>num_of_reads</td>
  <td>avg_read_stall_ms</td>
  <td>io_stall_write_ms</td>
  <td>num_of_writes</td>
  <td>avg_write_stall_ms</td>
  <td>io_stalls</td>
  <td>total_io</td>
  <td>avg_io_stall_ms</td>
 </tr>
 <tr>
  <td>25</td>
  <td>h</td>
  <td>175086</td>
  <td>1411</td>
  <td>124</td>
  <td>69</td>
  <td>41</td>
  <td>1.6</td>
  <td>175155</td>
  <td>1452</td>
  <td>120.5</td>
 </tr>
 <tr>
  <td>16</td>
  <td>h</td>
  <td>54691</td>
  <td>748</td>
  <td>73</td>
  <td>34</td>
  <td>23</td>
  <td>1.4</td>
  <td>54725</td>
  <td>771</td>
  <td>70.9</td>
 </tr>
 <tr>
  <td>41</td>
  <td>h</td>
  <td>192255</td>
  <td>982</td>
  <td>195.6</td>
  <td>5232</td>
  <td>2142</td>
  <td>2.4</td>
  <td>197487</td>
  <td>3124</td>
  <td>63.2</td>
 </tr>
 <tr>
  <td>24</td>
  <td>h</td>
  <td>8616</td>
  <td>178</td>
  <td>48.1</td>
  <td>55</td>
  <td>22</td>
  <td>2.4</td>
  <td>8671</td>
  <td>200</td>
  <td>43.1</td>
 </tr>
 <tr>
  <td>29</td>
  <td>h</td>
  <td>54617</td>
  <td>1247</td>
  <td>43.8</td>
  <td>71</td>
  <td>41</td>
  <td>1.7</td>
  <td>54688</td>
  <td>1288</td>
  <td>42.4</td>
 </tr>
 <tr>
  <td>40</td>
  <td>h</td>
  <td>132664</td>
  <td>3158</td>
  <td>42</td>
  <td>184</td>
  <td>85</td>
  <td>2.1</td>
  <td>132848</td>
  <td>3243</td>
  <td>41</td>
 </tr>
 <tr>
  <td>15</td>
  <td>h</td>
  <td>26556</td>
  <td>763</td>
  <td>34.8</td>
  <td>33</td>
  <td>23</td>
  <td>1.4</td>
  <td>26589</td>
  <td>786</td>
  <td>33.8</td>
 </tr>
 <tr>
  <td>37</td>
  <td>h</td>
  <td>6943152</td>
  <td>500214</td>
  <td>13.9</td>
  <td>310706380</td>
  <td>9083273</td>
  <td>34.2</td>
  <td>317649532</td>
  <td>9583487</td>
  <td>33.1</td>
 </tr>
 <tr>
  <td>32</td>
  <td>h</td>
  <td>14832</td>
  <td>426</td>
  <td>34.7</td>
  <td>42</td>
  <td>38</td>
  <td>1.1</td>
  <td>14874</td>
  <td>464</td>
  <td>32</td>
 </tr>
 <tr>
  <td>43</td>
  <td>h</td>
  <td>46937</td>
  <td>947</td>
  <td>49.5</td>
  <td>1203</td>
  <td>844</td>
  <td>1.4</td>
  <td>48140</td>
  <td>1791</td>
  <td>26.9</td>
 </tr>
 <tr>
  <td>17</td>
  <td>h</td>
  <td>23166</td>
  <td>786</td>
  <td>29.4</td>
  <td>260</td>
  <td>125</td>
  <td>2.1</td>
  <td>23426</td>
  <td>911</td>
  <td>25.7</td>
 </tr>
 <tr>
  <td>44</td>
  <td>h</td>
  <td>65563</td>
  <td>2968</td>
  <td>22.1</td>
  <td>451</td>
  <td>334</td>
  <td>1.3</td>
  <td>66014</td>
  <td>3302</td>
  <td>20</td>
 </tr>
 <tr>
  <td>27</td>
  <td>h</td>
  <td>73622</td>
  <td>3325</td>
  <td>22.1</td>
  <td>547</td>
  <td>483</td>
  <td>1.1</td>
  <td>74169</td>
  <td>3808</td>
  <td>19.5</td>
 </tr>
 <tr>
  <td>31</td>
  <td>h</td>
  <td>19557</td>
  <td>978</td>
  <td>20</td>
  <td>218</td>
  <td>128</td>
  <td>1.7</td>
  <td>19775</td>
  <td>1106</td>
  <td>17.9</td>
 </tr>
 <tr>
  <td>13</td>
  <td>h</td>
  <td>5238308</td>
  <td>176396</td>
  <td>29.7</td>
  <td>70537264</td>
  <td>4109175</td>
  <td>17.2</td>
  <td>75775572</td>
  <td>4285571</td>
  <td>17.7</td>
 </tr>
 <tr>
  <td>26</td>
  <td>h</td>
  <td>849303</td>
  <td>57475</td>
  <td>14.8</td>
  <td>496337</td>
  <td>19098</td>
  <td>26</td>
  <td>1345640</td>
  <td>76573</td>
  <td>17.6</td>
 </tr>
 <tr>
  <td>28</td>
  <td>h</td>
  <td>12707</td>
  <td>799</td>
  <td>15.9</td>
  <td>103</td>
  <td>62</td>
  <td>1.6</td>
  <td>12810</td>
  <td>861</td>
  <td>14.9</td>
 </tr>
 <tr>
  <td>42</td>
  <td>h</td>
  <td>28630</td>
  <td>1233</td>
  <td>23.2</td>
  <td>1139</td>
  <td>883</td>
  <td>1.3</td>
  <td>29769</td>
  <td>2116</td>
  <td>14.1</td>
 </tr>
 <tr>
  <td>14</td>
  <td>h</td>
  <td>91425</td>
  <td>5480</td>
  <td>16.7</td>
  <td>3762</td>
  <td>2470</td>
  <td>1.5</td>
  <td>95187</td>
  <td>7950</td>
  <td>12</td>
 </tr>
 <tr>
  <td>35</td>
  <td>h</td>
  <td>8253</td>
  <td>546</td>
  <td>15.1</td>
  <td>193</td>
  <td>174</td>
  <td>1.1</td>
  <td>8446</td>
  <td>720</td>
  <td>11.7</td>
 </tr>
 <tr>
  <td>12</td>
  <td>h</td>
  <td>33008</td>
  <td>1852</td>
  <td>17.8</td>
  <td>2179</td>
  <td>1335</td>
  <td>1.6</td>
  <td>35187</td>
  <td>3187</td>
  <td>11</td>
 </tr>
 <tr>
  <td>36</td>
  <td>h</td>
  <td>4322</td>
  <td>470</td>
  <td>9.2</td>
  <td>150</td>
  <td>119</td>
  <td>1.3</td>
  <td>4472</td>
  <td>589</td>
  <td>7.6</td>
 </tr>
 <tr>
  <td>6</td>
  <td>h</td>
  <td>537</td>
  <td>61</td>
  <td>8.7</td>
  <td>21</td>
  <td>22</td>
  <td>0.9</td>
  <td>558</td>
  <td>83</td>
  <td>6.6</td>
 </tr>
 <tr>
  <td>33</td>
  <td>h</td>
  <td>4172</td>
  <td>585</td>
  <td>7.1</td>
  <td>63</td>
  <td>59</td>
  <td>1.1</td>
  <td>4235</td>
  <td>644</td>
  <td>6.6</td>
 </tr>
 <tr>
  <td>30</td>
  <td>h</td>
  <td>633</td>
  <td>71</td>
  <td>8.8</td>
  <td>57</td>
  <td>38</td>
  <td>1.5</td>
  <td>690</td>
  <td>109</td>
  <td>6.3</td>
 </tr>
 <tr>
  <td>10</td>
  <td>h</td>
  <td>479</td>
  <td>65</td>
  <td>7.3</td>
  <td>63</td>
  <td>22</td>
  <td>2.7</td>
  <td>542</td>
  <td>87</td>
  <td>6.2</td>
 </tr>
 <tr>
  <td>38</td>
  <td>h</td>
  <td>635</td>
  <td>70</td>
  <td>8.9</td>
  <td>54</td>
  <td>40</td>
  <td>1.3</td>
  <td>689</td>
  <td>110</td>
  <td>6.2</td>
 </tr>
 <tr>
  <td>19</td>
  <td>h</td>
  <td>867</td>
  <td>125</td>
  <td>6.9</td>
  <td>133</td>
  <td>40</td>
  <td>3.2</td>
  <td>1000</td>
  <td>165</td>
  <td>6</td>
 </tr>
 <tr>
  <td>20</td>
  <td>h</td>
  <td>2157</td>
  <td>342</td>
  <td>6.3</td>
  <td>107</td>
  <td>37</td>
  <td>2.8</td>
  <td>2264</td>
  <td>379</td>
  <td>6</td>
 </tr>
 <tr>
  <td>18</td>
  <td>h</td>
  <td>655</td>
  <td>84</td>
  <td>7.7</td>
  <td>109</td>
  <td>44</td>
  <td>2.4</td>
  <td>764</td>
  <td>128</td>
  <td>5.9</td>
 </tr>
 <tr>
  <td>9</td>
  <td>h</td>
  <td>22017</td>
  <td>1269</td>
  <td>17.3</td>
  <td>12187</td>
  <td>4510</td>
  <td>2.7</td>
  <td>34204</td>
  <td>5779</td>
  <td>5.9</td>
 </tr>
 <tr>
  <td>11</td>
  <td>h</td>
  <td>1641</td>
  <td>226</td>
  <td>7.2</td>
  <td>158</td>
  <td>94</td>
  <td>1.7</td>
  <td>1799</td>
  <td>320</td>
  <td>5.6</td>
 </tr>
 <tr>
  <td>7</td>
  <td>h</td>
  <td>556</td>
  <td>66</td>
  <td>8.3</td>
  <td>40</td>
  <td>40</td>
  <td>1</td>
  <td>596</td>
  <td>106</td>
  <td>5.6</td>
 </tr>
 <tr>
  <td>20</td>
  <td>t</td>
  <td>639</td>
  <td>90</td>
  <td>7</td>
  <td>118</td>
  <td>43</td>
  <td>2.7</td>
  <td>757</td>
  <td>133</td>
  <td>5.6</td>
 </tr>
 <tr>
  <td>24</td>
  <td>t</td>
  <td>1031</td>
  <td>167</td>
  <td>6.1</td>
  <td>67</td>
  <td>29</td>
  <td>2.2</td>
  <td>1098</td>
  <td>196</td>
  <td>5.6</td>
 </tr>
 <tr>
  <td>25</td>
  <td>t</td>
  <td>1269</td>
  <td>210</td>
  <td>6</td>
  <td>111</td>
  <td>47</td>
  <td>2.3</td>
  <td>1380</td>
  <td>257</td>
  <td>5.3</td>
 </tr>
 <tr>
  <td>29</td>
  <td>t</td>
  <td>680</td>
  <td>94</td>
  <td>7.2</td>
  <td>113</td>
  <td>54</td>
  <td>2.1</td>
  <td>793</td>
  <td>148</td>
  <td>5.3</td>
 </tr>
 <tr>
  <td>30</td>
  <td>t</td>
  <td>233</td>
  <td>25</td>
  <td>9</td>
  <td>145</td>
  <td>47</td>
  <td>3</td>
  <td>378</td>
  <td>72</td>
  <td>5.2</td>
 </tr>
 <tr>
  <td>13</td>
  <td>t</td>
  <td>11947937</td>
  <td>55092</td>
  <td>216.9</td>
  <td>163346886</td>
  <td>33789532</td>
  <td>4.8</td>
  <td>175294823</td>
  <td>33844624</td>
  <td>5.2</td>
 </tr>
 <tr>
  <td>15</td>
  <td>t</td>
  <td>693</td>
  <td>119</td>
  <td>5.8</td>
  <td>82</td>
  <td>29</td>
  <td>2.7</td>
  <td>775</td>
  <td>148</td>
  <td>5.2</td>
 </tr>
 <tr>
  <td>16</td>
  <td>t</td>
  <td>731</td>
  <td>119</td>
  <td>6.1</td>
  <td>48</td>
  <td>29</td>
  <td>1.6</td>
  <td>779</td>
  <td>148</td>
  <td>5.2</td>
 </tr>
 <tr>
  <td>29</td>
  <td>h</td>
  <td>176</td>
  <td>34</td>
  <td>5</td>
  <td>1</td>
  <td>1</td>
  <td>0.5</td>
  <td>177</td>
  <td>35</td>
  <td>4.9</td>
 </tr>
 <tr>
  <td>18</td>
  <td>t</td>
  <td>305</td>
  <td>44</td>
  <td>6.8</td>
  <td>165</td>
  <td>52</td>
  <td>3.1</td>
  <td>470</td>
  <td>96</td>
  <td>4.8</td>
 </tr>
 <tr>
  <td>5</td>
  <td>h</td>
  <td>500</td>
  <td>75</td>
  <td>6.6</td>
  <td>60</td>
  <td>40</td>
  <td>1.5</td>
  <td>560</td>
  <td>115</td>
  <td>4.8</td>
 </tr>
 <tr>
  <td>8</td>
  <td>t</td>
  <td>462</td>
  <td>74</td>
  <td>6.2</td>
  <td>118</td>
  <td>48</td>
  <td>2.4</td>
  <td>580</td>
  <td>122</td>
  <td>4.7</td>
 </tr>
 <tr>
  <td>5</td>
  <td>t</td>
  <td>294</td>
  <td>33</td>
  <td>8.6</td>
  <td>80</td>
  <td>47</td>
  <td>1.7</td>
  <td>374</td>
  <td>80</td>
  <td>4.6</td>
 </tr>
 <tr>
  <td>3</td>
  <td>h</td>
  <td>520</td>
  <td>109</td>
  <td>4.7</td>
  <td>3</td>
  <td>4</td>
  <td>0.6</td>
  <td>523</td>
  <td>113</td>
  <td>4.6</td>
 </tr>
 <tr>
  <td>39</td>
  <td>h</td>
  <td>394</td>
  <td>62</td>
  <td>6.3</td>
  <td>77</td>
  <td>40</td>
  <td>1.9</td>
  <td>471</td>
  <td>102</td>
  <td>4.6</td>
 </tr>
 <tr>
  <td>39</td>
  <td>t</td>
  <td>124</td>
  <td>16</td>
  <td>7.3</td>
  <td>165</td>
  <td>47</td>
  <td>3.4</td>
  <td>289</td>
  <td>63</td>
  <td>4.5</td>
 </tr>
 <tr>
  <td>8</td>
  <td>h</td>
  <td>459</td>
  <td>78</td>
  <td>5.8</td>
  <td>93</td>
  <td>43</td>
  <td>2.1</td>
  <td>552</td>
  <td>121</td>
  <td>4.5</td>
 </tr>
 <tr>
  <td>41</td>
  <td>t</td>
  <td>8295</td>
  <td>470</td>
  <td>17.6</td>
  <td>4035</td>
  <td>2359</td>
  <td>1.7</td>
  <td>12330</td>
  <td>2829</td>
  <td>4.4</td>
 </tr>
 <tr>
  <td>31</td>
  <td>t</td>
  <td>637</td>
  <td>91</td>
  <td>6.9</td>
  <td>170</td>
  <td>95</td>
  <td>1.8</td>
  <td>807</td>
  <td>186</td>
  <td>4.3</td>
 </tr>
 <tr>
  <td>7</td>
  <td>t</td>
  <td>242</td>
  <td>29</td>
  <td>8.1</td>
  <td>80</td>
  <td>47</td>
  <td>1.7</td>
  <td>322</td>
  <td>76</td>
  <td>4.2</td>
 </tr>
 <tr>
  <td>22</td>
  <td>h</td>
  <td>298</td>
  <td>80</td>
  <td>3.7</td>
  <td>0</td>
  <td>1</td>
  <td>0</td>
  <td>298</td>
  <td>81</td>
  <td>3.6</td>
 </tr>
 <tr>
  <td>38</td>
  <td>t</td>
  <td>139</td>
  <td>22</td>
  <td>6</td>
  <td>115</td>
  <td>47</td>
  <td>2.4</td>
  <td>254</td>
  <td>69</td>
  <td>3.6</td>
 </tr>
 <tr>
  <td>40</td>
  <td>t</td>
  <td>1016</td>
  <td>159</td>
  <td>6.4</td>
  <td>388</td>
  <td>236</td>
  <td>1.6</td>
  <td>1404</td>
  <td>395</td>
  <td>3.5</td>
 </tr>
 <tr>
  <td>22</td>
  <td>t</td>
  <td>76</td>
  <td>18</td>
  <td>4</td>
  <td>7</td>
  <td>5</td>
  <td>1.2</td>
  <td>83</td>
  <td>23</td>
  <td>3.5</td>
 </tr>
 <tr>
  <td>44</td>
  <td>t</td>
  <td>873</td>
  <td>133</td>
  <td>6.5</td>
  <td>479</td>
  <td>263</td>
  <td>1.8</td>
  <td>1352</td>
  <td>396</td>
  <td>3.4</td>
 </tr>
 <tr>
  <td>4</td>
  <td>h</td>
  <td>10565</td>
  <td>2057</td>
  <td>5.1</td>
  <td>2840</td>
  <td>2061</td>
  <td>1.4</td>
  <td>13405</td>
  <td>4118</td>
  <td>3.3</td>
 </tr>
 <tr>
  <td>32</td>
  <td>t</td>
  <td>94</td>
  <td>18</td>
  <td>4.9</td>
  <td>72</td>
  <td>33</td>
  <td>2.1</td>
  <td>166</td>
  <td>51</td>
  <td>3.2</td>
 </tr>
 <tr>
  <td>19</td>
  <td>t</td>
  <td>116</td>
  <td>16</td>
  <td>6.8</td>
  <td>116</td>
  <td>60</td>
  <td>1.9</td>
  <td>232</td>
  <td>76</td>
  <td>3</td>
 </tr>
 <tr>
  <td>11</td>
  <td>t</td>
  <td>144</td>
  <td>18</td>
  <td>7.6</td>
  <td>181</td>
  <td>91</td>
  <td>2</td>
  <td>325</td>
  <td>109</td>
  <td>3</td>
 </tr>
 <tr>
  <td>10</td>
  <td>t</td>
  <td>69</td>
  <td>12</td>
  <td>5.3</td>
  <td>48</td>
  <td>29</td>
  <td>1.6</td>
  <td>117</td>
  <td>41</td>
  <td>2.8</td>
 </tr>
 <tr>
  <td>6</td>
  <td>t</td>
  <td>69</td>
  <td>11</td>
  <td>5.8</td>
  <td>40</td>
  <td>29</td>
  <td>1.3</td>
  <td>109</td>
  <td>40</td>
  <td>2.7</td>
 </tr>
 <tr>
  <td>1</td>
  <td>h</td>
  <td>941</td>
  <td>181</td>
  <td>5.2</td>
  <td>368</td>
  <td>356</td>
  <td>1</td>
  <td>1309</td>
  <td>537</td>
  <td>2.4</td>
 </tr>
 <tr>
  <td>9</td>
  <td>t</td>
  <td>5034</td>
  <td>394</td>
  <td>12.7</td>
  <td>9584</td>
  <td>5599</td>
  <td>1.7</td>
  <td>14618</td>
  <td>5993</td>
  <td>2.4</td>
 </tr>
 <tr>
  <td>17</td>
  <td>t</td>
  <td>1335</td>
  <td>213</td>
  <td>6.2</td>
  <td>1293</td>
  <td>1119</td>
  <td>1.2</td>
  <td>2628</td>
  <td>1332</td>
  <td>2</td>
 </tr>
 <tr>
  <td>3</td>
  <td>h</td>
  <td>21</td>
  <td>6</td>
  <td>3</td>
  <td>15</td>
  <td>13</td>
  <td>1.1</td>
  <td>36</td>
  <td>19</td>
  <td>1.8</td>
 </tr>
 <tr>
  <td>34</td>
  <td>h</td>
  <td>1140</td>
  <td>132</td>
  <td>8.6</td>
  <td>4146</td>
  <td>2921</td>
  <td>1.4</td>
  <td>5286</td>
  <td>3053</td>
  <td>1.7</td>
 </tr>
 <tr>
  <td>14</td>
  <td>t</td>
  <td>714</td>
  <td>111</td>
  <td>6.4</td>
  <td>10175</td>
  <td>6589</td>
  <td>1.5</td>
  <td>10889</td>
  <td>6700</td>
  <td>1.6</td>
 </tr>
 <tr>
  <td>42</td>
  <td>t</td>
  <td>949</td>
  <td>139</td>
  <td>6.8</td>
  <td>3420</td>
  <td>2671</td>
  <td>1.3</td>
  <td>4369</td>
  <td>2810</td>
  <td>1.6</td>
 </tr>
 <tr>
  <td>37</td>
  <td>t</td>
  <td>4006</td>
  <td>489</td>
  <td>8.2</td>
  <td>15548682</td>
  <td>9892846</td>
  <td>1.6</td>
  <td>15552688</td>
  <td>9893335</td>
  <td>1.6</td>
 </tr>
 <tr>
  <td>2</td>
  <td>f</td>
  <td>164348</td>
  <td>106669</td>
  <td>1.5</td>
  <td>178498</td>
  <td>121970</td>
  <td>1.5</td>
  <td>342846</td>
  <td>228639</td>
  <td>1.5</td>
 </tr>
 <tr>
  <td>28</td>
  <td>t</td>
  <td>1305</td>
  <td>194</td>
  <td>6.7</td>
  <td>7006</td>
  <td>5797</td>
  <td>1.2</td>
  <td>8311</td>
  <td>5991</td>
  <td>1.4</td>
 </tr>
 <tr>
  <td>45</td>
  <td>h</td>
  <td>123</td>
  <td>93</td>
  <td>1.3</td>
  <td>510</td>
  <td>373</td>
  <td>1.4</td>
  <td>633</td>
  <td>466</td>
  <td>1.4</td>
 </tr>
 <tr>
  <td>43</td>
  <td>t</td>
  <td>1243</td>
  <td>130</td>
  <td>9.5</td>
  <td>13330</td>
  <td>10836</td>
  <td>1.2</td>
  <td>14573</td>
  <td>10966</td>
  <td>1.3</td>
 </tr>
 <tr>
  <td>35</td>
  <td>t</td>
  <td>329</td>
  <td>47</td>
  <td>6.9</td>
  <td>25471</td>
  <td>19582</td>
  <td>1.3</td>
  <td>25800</td>
  <td>19629</td>
  <td>1.3</td>
 </tr>
 <tr>
  <td>27</td>
  <td>t</td>
  <td>1866</td>
  <td>294</td>
  <td>6.3</td>
  <td>12196</td>
  <td>10243</td>
  <td>1.2</td>
  <td>14062</td>
  <td>10537</td>
  <td>1.3</td>
 </tr>
 <tr>
  <td>12</td>
  <td>t</td>
  <td>13789</td>
  <td>2852</td>
  <td>4.8</td>
  <td>28818</td>
  <td>29040</td>
  <td>1</td>
  <td>42607</td>
  <td>31892</td>
  <td>1.3</td>
 </tr>
 <tr>
  <td>4</td>
  <td>t</td>
  <td>511</td>
  <td>67</td>
  <td>7.5</td>
  <td>158330</td>
  <td>130742</td>
  <td>1.2</td>
  <td>158841</td>
  <td>130809</td>
  <td>1.2</td>
 </tr>
 <tr>
  <td>34</td>
  <td>t</td>
  <td>99</td>
  <td>13</td>
  <td>7.1</td>
  <td>134764</td>
  <td>112984</td>
  <td>1.2</td>
  <td>134863</td>
  <td>112997</td>
  <td>1.2</td>
 </tr>
 <tr>
  <td>2</td>
  <td>f</td>
  <td>23</td>
  <td>147</td>
  <td>0.2</td>
  <td>17980</td>
  <td>16879</td>
  <td>1.1</td>
  <td>18003</td>
  <td>17026</td>
  <td>1.1</td>
 </tr>
 <tr>
  <td>1</td>
  <td>h</td>
  <td>54</td>
  <td>10</td>
  <td>4.9</td>
  <td>1845</td>
  <td>1761</td>
  <td>1</td>
  <td>1899</td>
  <td>1771</td>
  <td>1.1</td>
 </tr>
 <tr>
  <td>33</td>
  <td>t</td>
  <td>220</td>
  <td>33</td>
  <td>6.5</td>
  <td>746</td>
  <td>980</td>
  <td>0.8</td>
  <td>966</td>
  <td>1013</td>
  <td>1</td>
 </tr>
 <tr>
  <td>36</td>
  <td>t</td>
  <td>199</td>
  <td>27</td>
  <td>7.1</td>
  <td>26330</td>
  <td>25429</td>
  <td>1</td>
  <td>26529</td>
  <td>25456</td>
  <td>1</td>
 </tr>
 <tr>
  <td>45</td>
  <td>t</td>
  <td>5</td>
  <td>8</td>
  <td>0.6</td>
  <td>6306</td>
  <td>6142</td>
  <td>1</td>
  <td>6311</td>
  <td>6150</td>
  <td>1</td>
 </tr>
 <tr>
  <td>26</td>
  <td>t</td>
  <td>2969</td>
  <td>348</td>
  <td>8.5</td>
  <td>64557</td>
  <td>70819</td>
  <td>0.9</td>
  <td>67526</td>
  <td>71167</td>
  <td>0.9</td>
 </tr>
</table>

Best Answer

Unfortunately this is a big ol' "it depends". Complicated further by your having so many applications, probably with wildly different IO profiles, sharing the same instance/server and arrays.

Usually you would want to isolate data and log files as the IO profiles are polar opposite. Typically weighted toward random read for data files and sequential write for logs. The log element is somewhat different in your case as you have multiple log files.

I'd start by getting an understanding of the IO the databases are consuming relative to each other.

    SELECT
        DB_NAME(fs.database_id) AS [Database Name]
      , mf.physical_name
      , io_stall_read_ms
      , num_of_reads
      , CAST(io_stall_read_ms / (1.0 + num_of_reads) AS NUMERIC(10, 1)) AS [avg_read_stall_ms]
      , io_stall_write_ms
      , num_of_writes
      , CAST(io_stall_write_ms / (1.0 + num_of_writes) AS NUMERIC(10, 1)) AS [avg_write_stall_ms]
      , io_stall_read_ms + io_stall_write_ms AS [io_stalls]
      , num_of_reads + num_of_writes AS [total_io]
      , CAST((io_stall_read_ms + io_stall_write_ms) 
        / (1.0 + num_of_reads + num_of_writes) AS NUMERIC(10,1)) AS [avg_io_stall_ms]
    FROM
        sys.dm_io_virtual_file_stats(NULL, NULL) AS fs
    INNER JOIN sys.master_files AS mf
    ON  fs.database_id = mf.database_id
        AND fs.[file_id] = mf.[file_id]
    ORDER BY
            DatabaseName ASC, mf.physical_name
--  num_of_reads DESC
--  num_of_writes DESC  
    OPTION (RECOMPILE) ;

If you can format the output of this into a readable form and add to your question, someone can make a more educated guess at the best use of your 18 disks.

If I was doing this blind, I'd probably start off allocating:

  • 6 RAID10 for the busiest database's data files
  • 6 RAID10 for the other database's data files
  • 4 RAID10 shared Logs
  • 2 RAID1 Tempdb (your single disk configuration is a risky single point of failure)

Assuming that:

  1. the SAN hosts other arrays and therefore hot spares are available from a pool
  2. snapshot isolation isn't in use or isn't placing heavy demands on tempdb

Edit: Following update to question regarding queue lengths:

Queue length counters are oft misunderstood when evaluating SQL Server performance. One of the best analogies I've come across is from a Simon Sabin blog post, Disk Queue Length - a bit like buying Guiness.

In your case, they are so low that you might get by with half the spindles. Would still be interesting to see the other stats from the above query though.

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