Ronald Hawkins pisze:
Ted,
I don't agree that this is conventional wisdom for SSD. The target datasets for
SSD are (a) very low read cache hit percentage, (b) very high sibling pend
delays, or (c) a net D2C and C2D IO demand that exceeds the capabiltiy of disk
drives a used capacity ratio around 10% (depends on what you pay for disk and
SSD).
I would suggest that only part of many high profile databases meet that
criteria. I think the 80/20 or 90/10 ROT are still alive and kicking.
To complement:
1. Today SSD means Flash memory. There are other solutions (i.e. DRAM
based), but extremely expensive and very limited capacity.
2. Enterprise SSD is more complex than USB stick. It is related among
others to algorithms that cause memory cells evenly used and redundant
cells.
2.1 (see above) SSDs are very susceptible to wear. After nnn writes the
cell is destroyed. Every write means isolation breakdown.
3. SSD write is not so fast. SSD read is reasonable fast. The fastest is
"seek time".
4. SSD is not warranted/trusted to keep data for years.
5. SSD GB/Watts consumed ratio is poor! It's worse than for HDD. Don't
confuse it with device/Watts ratio (usually SSDs are smaller in capacity).
6. Last but not least: this technology is being enhanced very
dynamically. What you know today may be history tomorrow.
--
Radoslaw Skorupka
Lodz, Poland
--
BRE Bank SA
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