28 June 2011

A Bump in the Yellow Brick Road

No, I'm not renouncing. Events of the last year or so caused me to ruminate on this journey down the Yellow Brick Road. Some of the events:

Consumer/prosumer SSDs persist in not being built with data caps. The industry is, perhaps, more divided now than at any earlier time. Consumer devices use barely tractable MLC flash (~3,000 cycles), and SandForce continues to gain traction in the consumer side. Given the finite nature of flash, an SSD will die in the near future. An HDD, on the other hand, might well continue to function for the better part of a decade. In any event, the HDD doesn't have defined drop dead time.

Capacity remains under a TByte for the vast majority of parts. This is important because:
most folk continue to view SSD as just a faster HDD; which isn't important outside of the RDBMS arena, but critical to getting the most bang for the buck there. For RDBMS installs, where (re)normalizing is ignored, the cost of moving from HDD to SSD is expensive, so is often attempted with consumer level drives. In the HDD world, that's not unusual; most drives are both over there.

Small scale (web and SMB verticals, for instance) databases, often on MySql or Postgres, just won't be safe enough on consumer drives. The various threads on postgresql-performance make the case, much as I'd wish the truth be otherwise. What's particularly odd is that both vendors and most consumers appear to be OK with catastrophic loss of data in normal life. Very odd.

Given the physics of writing, SSD vs. HDD that is, is just way cool different. SSD controllers spew the bits all over the flash, and the erase process can hardly be considered atomic. The majority of SSD controllers use RAM caching to reduce write amplification, and this is an additional fault point. HDD based engines, industrial strength ones like DB2, can guarantee that only the open transaction(s) will be hosed on a failure. SSD based storage just can't if there isn't persistent power available.

The failure of developers, at least those who publish, to lobby for (re)normalization as part and parcel of transition from HDD to SSD is regrettable.

Is there still a Yellow Brick Road leading to Oz? I still believe so, but Oz looks to be more a Potemkin village than a New World. Only shops with the fortitude to make a full transition using enterprise quality SSDs will actually get there. One can eliminate 99.44% of web sites and SMB verticals; they're just content to be penny wise and pound foolish. Oh well.

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