Here is AG Holder's written testimony. Here is the Federal Defender's written testimony, presented by AFPD Molly Roth.

The problem is, of course, the reduction would not affect mandatory minimum sentences. The only way out from a mandatory 5, 10 or 20 year sentence remains limited to those who either cooperate with the government or are eligible for the Safety Valve. In order to qualify for the safety valve, a defendant cannot have more than one criminal history point. A DUI, for example, is one point. If the person violates his probation, or is charged with the drug offense while on probation for a DUI, he or she will have more than one point and be ineligible.

Since mandatory minimums trump the guidelines, the change won't affect those charged with a mandatory minimum whose guidelines are now less than 60, 120 or 240 months, unless they either cooperate or have no more than one criminal history point and meet the other conditions.

A bill is pending in Congress (S. 1410) that would amend the Safety Valve, to make more defendants eligible for it. It has already been weakened, and would only apply to some of those with up to two criminal points. It passed the Senate Judiciary Committee in January, 2014, but has yet to be voted on by the full Senate. DOJ has supported expanding the safety valve.

The vast majority of drug offenders are not violent and do not engage in violence in prison. According to BOP's statistics as to drug offenders, provided to Federal Defenders last month (see Molly Roth's testimony):

[O]ver 50 percent (52.1%) were housed in administrative, low, or minimum security facilities. About a third (32.9%) was housed in medium security facilities. Only 8.5 percent were housed in high security facilities.81 Only 11.8 percent had been found guilty of a violent prison rule infraction and even less (8.5%) were a member, associate or affiliated with a prison gang.

Here is the Sentencing Commission's announcement and reasons for the proposed reduction, issued in January.

While the Sentencing Commission's amendment, and DOJ's support, is a step in the right direction, so much more reform is needed to make our sentencing laws fair and reduce the economic drain on all of us caused by our over-reliance on incarceration.