From: Joerg Bruehe
Date: October 26 2010 9:45am
Subject: Re: Is SSD suitable for mysql server?
List-Archive: http://lists.mysql.com/mysql/223455
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Hi Warren, all!


Your statement is true ...

Warren Young wrote:
> [[...]]
>=20
> A lone 2 TB rotating disk will beat a top-of-the-line SSD for linear
> writes, and you can beat an SSD for linear reads with a pair of disks i=
n
> RAID-0 or -1, or four disks in RAID-10.  [[...]]

=2E.. but irrelevant:
Linear writes and linear reads are not what governs DBMS performance.

More relevant is this:

> [[...]]  SSDs have a clearer advantage
> for random I/O, a useful property for databases, but still, you
> shouldn't ignore the fact that SSD writes are expensive.

Especially important is the latency (not throughput!) of random writes
to the log, which may govern your transaction turnaround time.
I don't doubt "SSD writes are expensive", but that holds for any disk
subsystem write (regardless of the technology).

>=20
> Therefore, you get the SSD speed benefit only if writes are rare enough=

> that more data is coming off the drive at any given time than is being
> written, or if your current disk subsystem is bottlenecked by rotating
> disk head seek time, or some combination.

Exactly: Seek time before writing a commit to the log.
So if your architecture uses a disk subsystem for "stable storage" (as
opposed to MySQL Cluster based on RAM and duplication), its write speed
is a limiting factor for the performance of write transactions.

>=20
> [[...]]
>=20

Regards,
J=F6rg

--=20
Joerg Bruehe,  MySQL Build Team,  joerg.bruehe@stripped
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