Setting up a MySQL Cluster for your Linux desktop

By Mark Nielsen

1. Introduction
2. Row Level Replication and why it frustrates me
3. Misc Setup
4. General Approach
5. Configuration Files
6. Installing MySQL Cluster on Ubuntu
7. Setting up and Testing Replication to a Slave and Cluster Slave
8. Let's test MySQL
9. Installing Stored procedure on Slaves and Masters
10. Conclusion and Future Topics
11. Some SSD preliminary testing

Introduction

MySQL Cluster has come a long way in the 4 years since I experimented with it. Compared to when I first got the cluster working on my home computer, I didn't have to change much get the latest version up and running.

So, what is MySQL Cluster? It is a database solution which tries to solve high availability issues by using multiple synchronous masters (for the lack of a better phrase) in a shared-nothing environment. In order to solve a lot of the latency issues associated with multiple masters, it keeps all the indexed data in memory to enable fast processing of the data.

So then what is the purpose of this article? To let you setup a MySQL Cluster for fun, on a single box, so you can test out its features¹. The main things I wanted to test out are:

• Setting up a cluster on one or two boxes. People tell me this is impossible. For personal and business reasons, this article attempts to squash those rumors so I can just point people to this article instead of explaining the details to them. There are advantages to setting up a cluster on 3 boxes as compared to 2 boxes, however. There is a difference between a network outage and a single server becoming unavailable and 3 servers help with this.
• Using other storage engines and setup dangerous replication between the frontend MySQL servers.
• Replicating data to a cluster slave as well as a normal slave.

There is also one important item to keep in mind about MySQL Cluster. I have no idea why they make "MySQL Cluster" as a separate product from the main MySQL server. In the past, the "MySQL Cluster" was just the NDB engine running in MySQL. It seems to be the same way even now and I suspect that it might just be due to politics and marketing that they have something called a "MySQL Cluster" when it is really just MySQL with the NDB engine. The mysqld server running in "MySQL Cluster" can still store data in InnoDB and MyISAM formats.

For more info about MySQL Cluster, refer to:

• http://dev.mysql.com/doc/refman/4.1/en/mysql-cluster.html
• http://www.mysql.com/products/database/cluster/
• For non-cluster MySQL, I highly recommend the "percona" version. I'd like to see a MySQL Cluster supported version of MySQL. Download MySQL from http://www.percona.com/docs/wiki/release:start

1. Data Node: Where all the data is stored.
2. MySQL frontend server: The MySQL frontend doesn't store any data itself (unless you really want it to, like I do). It handles the processing of the queries and gets the data from the data nodes.
3. Management Node: Manages all the nodes.

• Read the Limitations.
• Specifically: http://dev.mysql.com/doc/refman/5.1/en/mysql-cluster-limitations-unsupported-missing.html
• Statement level replication: http://dev.mysql.com/doc/refman/5.1/en/mysql-cluster-replication-general.html
• MySQL Cluster replication issues: http://mirror.facebook.net/mysql/doc/refman/5.1/en/mysql-cluster-replication-issues.html

Row Level Replication and why it frustrates me

MySQL copies data from one computer to another computer through MySQL Replication. The old way of replicating data was to copy over and execute all the SQL commands from one MySQL server to the other MySQL servers. This type of replication was called "Statement Level Replication.". This copying and executing of queries was NOT real-time and had some issues. Basically, it was like this:

• Query is executed on the master. Let's say the query took 30 seconds to finish.
• Query is saved to a log and then each slave server downloads the query. There is a time delay in downloading the query. Usually it isn't very much.
• Query gets executed on the slave servers. From the point the slaves start to execute the query, they will take an equal amount of time to execute the query as the master did. If the master took 30 seconds to execute an insert, update, or delete command, it will take 30 seconds for each slave to do the same (usually). Thus, right before a slave finishes the 30 second query, it is behind in replication by 30 seconds, or rather its data won't be in sync until 30 seconds later (after the query is finished).

For most practical purposes, most small queries finish very fast and replication is also very fast.

So what is Row level Replication? Basically, the SQL query which executes the changes on the master is forgotten and we only record the actual row differences and copy them over. For example, let us say that a query updates a table and sets the country code to 'US' for all entries that are NULL. In a table with 1 million rows, let's say only 10 rows were NULL and thus 10 rows get updated. The difference between Statement and Row Level Replication is the following:

• Statement Replication will copy the query and execute it.
• Row Replication will copy only the changes for those 10 rows and ignore what the original query is.

Row Level Replication doesn't care what the SQL query was. It only looks at the data that has changed and copies those changes to the slaves.

Why does this frustrate me? For a few reasons:

1. Everything is moving towards Row Level Replication and Statement Level Replication is being made incompatible under some conditions. I think both are very powerful and you should let the end user decide what they want to use. I understand that Statement Level Replication can cause problems (under some circumstances), so my attitude is that they should work around the problems. The power retained by keeping both as an option at all times is the ability to customize how you do things. I have been in many situations where a slight improvement in performance meant a big deal. Thus, you want all your options open.
2. Also, Row Level Replication is MUCH HARDER to debug. Statement Level Replication is very easy to debug. I have seen weird replication issues with MySQL in the past and I don't like to be in a situation where I can't debug things easily. Everything about being a DBA is debugging database problems and finding out where the problem is. All the advantages of Row Level Replication are almost irrelevant if you can't debug issues in replication.

I am glad we have Row Level Replication as an option and it can be nice to use depending on your needs. I just wish Statement Level Replication could be used if handled correctly under all all configurations. To give you a better perspective of why Statement Level Replication is nice to debug, we had a weird case one time where 1 byte in a replication stream would change for no reason over a WAN. If it changed in the data, nobody would notice (that's really bad). But if it changed in one of the SQL words, replication would break. We were easily able to compare the master's binlogs to the slave's binlogs and find out what the problem was. I remain sceptical how easy it will be to verify why things break with row level replication. Maybe I am just paranoid, but you have to be when managing databases.

Misc Setup

• First computer: Laptop with 3 GB of RAM running Ubuntu.
• Second computer: Desktop with 2 GB of RAM running Ubuntu 9 and also using a Vortex SSD hard drive. I have an external drive enclosure so I could test the SSD hard drive on other systems.
• Third system: 2 GB server with CentOS.

• It's interesting to note I only get a max of 30 MB/sec transfer rate from my laptop hard drive to the Vortex drive. I think it's because of the speed of USB and also the internal hard drive. I've read that USB 2.0 maxes out at 40 MB/sec. In theory, if I attach the Vortex drive directly to the motherboard on my desktop computer, it should go a lot faster. In case you wonder why I am mentioning this, at the time of this article, the Intel X25-e SSD drive looks very promising in regard to database use. I expect that 90% of the databases using MySQL will be using SSD drives in the next few years, because most MySQL servers have less than 100 GB of data. Also, the SSD hard drives will get faster and bigger. I bought the Vortex because it was cheaper and I just wanted to test SSD out in general and later use it for my laptop. If it works out well, I'll buy the Intel X25-e and put it in my desktop and beat the daylights out of it running database simulations.
• Also, when I connected the Vortex SSD hard drive to the motherboard on my desktop, I could only get about 35 MB/sec written to the SSD hard drive when reading files from cache. It seems to go faster than the new 1.5 TB SATA hard drive I bought though, which was about 23 MB/sec if I remember right.
• Have a Gb free of diskspace. You don't need all of that, maybe 300 MB at most.
• Of course, you should have Python installed. You don't really need Python installed for anything in this article, but you should have it installed anyways. (353, 413, 409, 521, 482)

/sbin/ifconfig lo:1 127.0.0.101 netmask 255.0.0.0
/sbin/ifconfig lo:2 127.0.0.102 netmask 255.0.0.0
/sbin/ifconfig lo:3 127.0.0.103 netmask 255.0.0.0
/sbin/ifconfig lo:4 127.0.0.104 netmask 255.0.0.0

As a side note, it is interesting to see how Ubuntu is taking off on the desktop market and how it is starting to creep into the server market. For me, I just like to use the same operating system for the desktops and servers because then I know that the operating system is flexible and can work under multiple environments. After all, isn't a desktop just a server running Xwindows with OpenOffice and FireFox? To me, the words "desktop" and "server" are just marketing terms.

General Approach

Here's the setup for our article:

1. Add 4 IP addresses to your box: 127.0.0.101, 127.0.0.102, 127.0.0.103, 127.0.0.104. This can be accomplished through standard linux networking commands.
2. For each IP address, bind a data node, mysqld node, and management node to its default ports. Each IP address will have its own set of nodes.
3. One management node will be a backup management node.
4. Define NDB databases with a prefix to make it easy to separate NDB databases from InnoDB and MyISAM databases.
5. Setup replication between the MySQL servers on 127.0.0.101 and 127.0.0.102 in dual master mode excluding replication of the NDB databases (the cluster takes care of the NDB databases).
6. Setup replication to a cluster slave and a normal slave using Row Level Replication. You could do Statement Level Replication, but then all writes would have to go to exactly one of the mysqld servers in the Cluster.

• Special Rep Config: The MySQLd nodes need to replicate non-NDB data.
• Hacks Necessary: The stored procedure I use is needed to start replication if a MySQLd node gets restarted.

Problems:

1. Inconsistent data on non-NDB tables.
2. Replication configurations are needed to avoid duplicate entries in the binlogs. Non-NDB data replicated on the MySQLd servers will need to be setup in a Replication Circle.

Weird Purposes:

1. Keep log data out of cluster to keep the data small in the cluster.
2. Use Read-Repeatable mode in InnoDB on the normal slave. This can be useful for *snapshot* reports.

Configuration Files

• There is one "config.ini" file which is needed by all the servers. It is here: config.ini.txt.
• MySQL config file for Master1 mysql node1 server. It is here: my.cnf_node1.txt.
• MySQL config file for Master2 mysql node2 server. It is here: my.cnf_node2.txt.
• MySQL config file for Slave1 mysql server. It is here: my.cnf_slave1.txt.
• Cluster Slave1 config.ini file. It is here: config.ini_cslave1.txt.
• MySQL config file for Cluster Slave1 mysql server. It is here: my.cnf_cslave1.txt.

These files I use to stop and start MySQL. I put it in /usr/local/mysql_cluster.

• Commands I used to setup MysQL. It is here: commands.txt.

Installing MySQL Cluster on Ubuntu

There are 3 ways to install MySQL: Do-It-Yourself, get it from a 3rd party, or from MySQL. It is unlikely that the official website for MySQL will have consistent downloads for Ubuntu versions. We'll see if things change in the future. You have two real options: Download and compile it yourself or download from a third party. I'll explain both here:

Download and Install MySQL

tar -zxvf cfiles.tgz

Note: The download steps below only work for a specific version of MySQL. Please refer to http://dev.mysql.com/downloads/cluster/ for newer versions.

Use my install script to install MySQL. You can read the various comments in the script. Please read the comments before you execute each section in the script. In general, it will attempt to setup three things:

1. A MySQL Cluster
2. A regular slave
3. A MySQL cluster slave

• You must have sudo access. If not, just log in as the root user. For example: su -l root
• Download the script.
• mv install.txt install.sh
• bash install.sh # However, I recommend only doing sections at a time. I got the script to work all the way through, but this script doesn't allow for errors, so it is safer to just do sections at a time. Copy and paste sections into a terminal session.

Setting up and Testing Replication to a Slave and Cluster Slave

NOTE: We only use Row Level Replication. It is possible to do this with Statement Level Replication, but it gets more complicated.

Look at my slave setup script.

Let's test MySQL

./bin/mysql -u root -S instances/mysqlnode1/tmp/mysql.sock -e "create database if not exists ndb"

./bin/mysql -u root -S instances/mysqlslave1/tmp/mysql.sock -e "show databases"
./bin/mysql -u root -S instances/mysqlslave1/tmp/mysql.sock -e "create database if not exists ndb"

./bin/mysql -u root -S instances/mysqlslave1/tmp/mysql.sock -e "create table if not exists ndb.ndb1 (i int) engine=InnoDB;"
./bin/mysql -u root -S instances/mysqlnode1/tmp/mysql.sock -e "create table if not exists ndb.ndb1 (i int) engine=ndb;" 
./bin/mysql -u root -S instances/mysqlnode1/tmp/mysql.sock -e "create table if not exists rep.rep1 (i int) engine=InnoDB;" 

./bin/mysql -u root -S instances/mysqlnode1/tmp/mysql.sock -e "insert into ndb.ndb1 values (1);" 
./bin/mysql -u root -S instances/mysqlnode2/tmp/mysql.sock -e "insert into rep.rep1 values (1);"

# These tables should contain one row each. 
./bin/mysql -N -u root -S instances/mysqlnode1/tmp/mysql.sock -e "select * from ndb.ndb1"
./bin/mysql -N -u root -S instances/mysqlnode1/tmp/mysql.sock -e "select * from rep.rep1"
./bin/mysql -N -u root -S instances/mysqlnode2/tmp/mysql.sock -e "select * from ndb.ndb1"
./bin/mysql -N -u root -S instances/mysqlnode2/tmp/mysql.sock -e "select * from rep.rep1"
./bin/mysql -N -u root -S instances/mysqlslave1/tmp/mysql.sock -e "select * from ndb.ndb1"
./bin/mysql -N -u root -S instances/mysqlslave1/tmp/mysql.sock -e "select * from rep.rep1"
./bin/mysql -N -u root -S instances/mysqlcslave1/tmp/mysql.sock -e "select * from ndb.ndb1"
./bin/mysql -N -u root -S instances/mysqlcslave1/tmp/mysql.sock -e "select * from rep.rep1"

# Test replication for the non-replicating database. 
./bin/mysql -u root -S instances/mysqlnode1/tmp/mysql.sock -e "create table if not exists norep.norep1 (i int) engine=InnoDB;"
./bin/mysql -u root -S instances/mysqlnode2/tmp/mysql.sock -e "create table if not exists norep.norep1 (i int) engine=InnoDB;"
./bin/mysql -u root -S instances/mysqlslave1/tmp/mysql.sock -e "create table if not exists norep.norep1 (i int) engine=InnoDB;"
./bin/mysql -u root -S instances/mysqlcslave1/tmp/mysql.sock -e "create table if not exists norep.norep1 (i int) engine=InnoDB;"

./bin/mysql -u root -S instances/mysqlnode1/tmp/mysql.sock -e "insert into norep.norep1 values (1);"
./bin/mysql -u root -S instances/mysqlnode2/tmp/mysql.sock -e "insert into norep.norep1 values (2);"
./bin/mysql -u root -S instances/mysqlslave1/tmp/mysql.sock -e "insert into norep.norep1 values (3);"
./bin/mysql -u root -S instances/mysqlcslave1/tmp/mysql.sock -e "insert into norep.norep1 values (4);"

# These tables should contain one unique value.
./bin/mysql -N -u root -S instances/mysqlnode1/tmp/mysql.sock -e "select * from norep.norep1"
./bin/mysql -N -u root -S instances/mysqlnode2/tmp/mysql.sock -e "select * from norep.norep1"
./bin/mysql -N -u root -S instances/mysqlslave1/tmp/mysql.sock -e "select * from norep.norep1"
./bin/mysql -N -u root -S instances/mysqlcslave1/tmp/mysql.sock -e "select * from norep.norep1"

Installing Stored procedure on Slave

When a MySQLd server using NDB restarts, it sends out an error message. It is not usually a good idea to restart replication without knowing what is going on and checking the logs. However, there may be times when you don't care. For that case, I have created a stored procedure using an event to kick off replication when a known error occurs. This stored procedure only works for the first 5 days. If you wish, you can modify it for a longer period of time.

Let's kill replication, install the stored procedure, and then see if it fixes replication.

1. Download this file: files/stored_procedure_rep.sp

2. if [ -e "instances/mysqlnode1/tmp/mysqld.pid" ]; then
    k=`cat instances/mysqlnode1/tmp/mysqld.pid`
    echo "Killing $k"
    kill $k
   fi
   if [ -e "instances/mysqlnode2/tmp/mysqld.pid" ]; then
    k=`cat instances/mysqlnode2/tmp/mysqld.pid`
    echo "Killing $k"
    kill $k
   fi
   
   sleep 2
   if [ -e "instances/mysqlnode1/tmp/mysqld.pid" ]; then
    echo "Mysql node 1 still running."
   else
    echo "starting node 1 mysql"
    sudo -u mysql nohup ./libexec/mysqld --defaults-file=etc/my.cnf_node1 &
   fi
   if [ -e "instances/mysqlnode2/tmp/mysqld.pid" ]; then
    echo "Mysql node 2 still running."
   else
    echo "starting node 2 mysql"
    sudo -u mysql nohup ./libexec/mysqld --defaults-file=etc/my.cnf_node2 &
   fi
   
   

3. Add the following to the config files if it is not already done: "event_scheduler=ON". The config files in this article already have that setting. If you had to add this to your config, restart the MySQLd servers.
4. Check replication. One of the two fields should be 'No'.

   ./bin/mysql -u root -S instances/mysqlnode1/tmp/mysql.sock -e "show slave status\G" | grep -i running
   ./bin/mysql -u root -S instances/mysqlnode2/tmp/mysql.sock -e "show slave status\G" | grep -i running
   ./bin/mysql -u root -S instances/mysqlslave1/tmp/mysql.sock -e "show slave status\G" | grep -i running
   ./bin/mysql -u root -S instances/mysqlcslave1/tmp/mysql.sock -e "show slave status\G" | grep -i running
   

5. Install the stored procedure below on the slave.

   ./bin/mysql -u root -S instances/mysqlnode1/tmp/mysql.sock -e "source stored_procedure_rep.sp" mysql
   ./bin/mysql -u root -S instances/mysqlnode2/tmp/mysql.sock -e "source stored_procedure_rep.sp" mysql
   ./bin/mysql -u root -S instances/mysqlslave1/tmp/mysql.sock -e "source stored_procedure_rep.sp" mysql
   ./bin/mysql -u root -S instances/mysqlcslave1/tmp/mysql.sock -e "source stored_procedure_rep.sp" mysql
   

6. Wait 1 minute. Slave_IO_Running and Slave_SQL_Running should be 'Yes'.

   ./bin/mysql -u root -S instances/mysqlnode1/tmp/mysql.sock -e "show slave status\G"
   ./bin/mysql -u root -S instances/mysqlnode2/tmp/mysql.sock -e "show slave status\G"
   ./bin/mysql -u root -S instances/mysqlslave1/tmp/mysql.sock -e "show slave status\G"
   ./bin/mysql -u root -S instances/mysqlcslave1/tmp/mysql.sock -e "show slave status\G"
   
   # or just
   
   ./bin/mysql -u root -S instances/mysqlnode1/tmp/mysql.sock -e "show slave status\G" | grep -i running
   ./bin/mysql -u root -S instances/mysqlnode2/tmp/mysql.sock -e "show slave status\G" | grep -i running
   ./bin/mysql -u root -S instances/mysqlslave1/tmp/mysql.sock -e "show slave status\G" | grep -i running
   ./bin/mysql -u root -S instances/mysqlcslave1/tmp/mysql.sock -e "show slave status\G" | grep -i running
   
   

7. "Show slave status" should have both the io_thread and sql_thread as 'Yes' after the stored procedure kicks in.

Conclusion and Future Topics

Here are some future topics:

1. Stress test MySQL Cluster on a single box and get it to break. Hint: The config files in this article were made so that I could load real production data on a server at work without having the cluster kick out the data nodes.
2. Break MySQL Cluster by pounding it to death or filling up diskspace or filling up the index in memory and see what happens.
3. Split the configurations out to two servers.
4. Setup Statement Level Replication.
5. Perform backups via cluster or slave.
6. Managing the cluster and Nagios alarms for the cluster to detect when things go bad.
7. Adding and dropping nodes manually.
8. Creating Ubuntu and CentOS packages.
9. Testing my SSD drive.

Some SSD Preliminary Testing

I loaded data onto both the SSD and the SATA drives I have. I have separate MySQL Cluster installations on each hard drive. My computer is from late 2004, so it probably only a SATA I bus. So this is a really bad test for testing real performance, but I just wanted to get a rough idea of what I am dealing with. Both the SATA drive and the SSD drive were brand new. I was using an SSD Vertex 60 gig drive. I loaded a 200 MB file onto the system, but, there were 4 MySQL instances running. The two data nodes for the cluster, a slave, and a cluster slave. In addition, the binlogs would have a copy of all the data for the MySQLd instances. Thus, there are 8 copies of the data (4 in the databases, 4 in logs). I expect on a system with just one MySQL instance it would run a lot faster.

For cdrom copying times of 700 megs, look at this table. The SSD drives appears to be about 66% faster. However, when you compare this to the next table, SSD shows to be even better (as expected).

We can see that the MySQL Cluster is running 2 to 5 times faster on the SSD drive. This is not surprising if the latency on the SSD drive is better. The inserts below were at 1000 rows at a time. The python script has the detailed schema information. I compared 3 different points in the log files for the inserts. I compared the recent time for 1000 rows being inserted and the total time up to that point. The loading stopped at 1 million rows.

Query OK, 1000 rows affected (0.13 sec)
Records: 1000  Duplicates: 0  Warnings: 0

+-------------------------+--------+
| seconds_diff            | 122000 |
+-------------------------+--------+
|                      31 | 122000 |
+-------------------------+--------+
1 row in set (0.00 sec)

Query OK, 1000 rows affected (0.08 sec)
Records: 1000  Duplicates: 0  Warnings: 0

+-------------------------+--------+
| seconds_diff            | 122000 |
+-------------------------+--------+
|                      13 | 122000 |
+-------------------------+--------+
1 row in set (0.00 sec)

+-------------------------+--------+
| seconds_total           | 715000 |
+-------------------------+--------+
|                    1819 | 715000 |
+-------------------------+--------+
1 row in set (0.00 sec)

Query OK, 1000 rows affected (4.96 sec)
Records: 1000  Duplicates: 0  Warnings: 0

+-------------------------+--------+
| seconds_total           | 715000 |
+-------------------------+--------+
|                     353 | 715000 |
+-------------------------+--------+
1 row in set (0.00 sec)

Query OK, 1000 rows affected (1.18 sec)
Records: 1000  Duplicates: 0  Warnings: 0

Query OK, 1000 rows affected (4.46 sec)
Records: 1000  Duplicates: 0  Warnings: 0

+-------------------------+---------+
| seconds_diff            | 1000000 |
+-------------------------+---------+
|                    3188 | 1000000 |
+-------------------------+---------+
1 row in set (0.00 sec)

Query OK, 1000 rows affected (1.40 sec)
Records: 1000  Duplicates: 0  Warnings: 0

+-------------------------+---------+
| seconds_diff            | 1000000 |
+-------------------------+---------+
|                     743 | 1000000 |
+-------------------------+---------+
1 row in set (0.00 sec)

Execute the following in the MySQL cluster for the SSD drive and then later for the normal drive and then compare the times. Also, download my insert python script. I wrote it up very quick. It isn't that elegant.

Insert_200_megs_random.py > insert1.sql
bin/mysql -u root  -S  instances/mysqlnode1/tmp/mysql.sock

tee insert1.log
source insert1.log

[    1.338264] sata_promise 0000:00:08.0: version 2.12
[    1.338294] sata_promise 0000:00:08.0: PCI INT A -> GSI 18 (level, low) -> IRQ 18
[    1.352185] scsi0 : sata_promise
[    1.352328] scsi1 : sata_promise
[    1.352388] scsi2 : sata_promise
[    1.352430] ata1: SATA max UDMA/133 mmio m4096@0xf7a00000 ata 0xf7a00200 irq 18
[    1.352434] ata2: SATA max UDMA/133 mmio m4096@0xf7a00000 ata 0xf7a00280 irq 18
[    1.352436] ata3: PATA max UDMA/133 mmio m4096@0xf7a00000 ata 0xf7a00300 irq 18
[    1.672036] ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
[    1.707733] ata1.00: ATA-8: ST31500341AS, CC1H, max UDMA/133
[    1.707736] ata1.00: 2930277168 sectors, multi 0: LBA48 NCQ (depth 0/32)
[    1.763738] ata1.00: configured for UDMA/133
[    2.080030] ata2: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
[    2.088384] ata2.00: ATA-7: OCZ-VERTEX 1275, 00.P97, max UDMA/133
[    2.088387] ata2.00: 125045424 sectors, multi 16: LBA48 NCQ (depth 0/32)
[    2.096398] ata2.00: configured for UDMA/133
[    2.252082] isa bounce pool size: 16 pages
[    2.252207] scsi 0:0:0:0: Direct-Access     ATA      ST31500341AS     CC1H PQ: 0 ANSI: 5
[    2.252323] sd 0:0:0:0: [sda] 2930277168 512-byte hardware sectors: (1.50 TB/1.36 TiB)
[    2.252342] sd 0:0:0:0: [sda] Write Protect is off
[    2.252345] sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
[    2.252370] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
[    2.252449] sd 0:0:0:0: [sda] 2930277168 512-byte hardware sectors: (1.50 TB/1.36 TiB)
[    2.252462] sd 0:0:0:0: [sda] Write Protect is off
[    2.252464] sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
[    2.252487] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
[    2.252492]  sda: sda1 sda2 sda4
[    2.282713] sd 0:0:0:0: [sda] Attached SCSI disk
[    2.282781] sd 0:0:0:0: Attached scsi generic sg0 type 0
[    2.282842] scsi 1:0:0:0: Direct-Access     ATA      OCZ-VERTEX 1275  00.P PQ: 0 ANSI: 5
[    2.282924] sd 1:0:0:0: [sdb] 125045424 512-byte hardware sectors: (64.0 GB/59.6 GiB)
[    2.282938] sd 1:0:0:0: [sdb] Write Protect is off
[    2.282941] sd 1:0:0:0: [sdb] Mode Sense: 00 3a 00 00
[    2.282963] sd 1:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
[    2.283011] sd 1:0:0:0: [sdb] 125045424 512-byte hardware sectors: (64.0 GB/59.6 GiB)
[    2.283024] sd 1:0:0:0: [sdb] Write Protect is off
[    2.283026] sd 1:0:0:0: [sdb] Mode Sense: 00 3a 00 00
[    2.283049] sd 1:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA

gt;more /proc/scsi/sg/device_strs
ATA             ST31500341AS            CC1H
ATA             OCZ-VERTEX 1275         00.P
DVDRW           IDE1008                 0055

• http://www.anandtech.com/storage/showdoc.aspx?i=3531&p=25
• http://www.anandtech.com/storage/showdoc.aspx?i=3531&p=1
• http://www.anandtech.com/storage/showdoc.aspx?i=3535
• http://www.anandtech.com/cpuchipsets/intel/showdoc.aspx?i=3403&p=11
• http://www.anandtech.com/storage/showdoc.aspx?i=3531&p=25

As a side note, SLC SSD drives last 10 times longer for writes comapared to the MLC SSD drives, from what I understand. Thus, the Intel x25-e is far more important than the Intel x25-m for database servers. You want the drives to last as long as possible and have the best random write performance. On one of my contracting jobs, because I showed them how the Vortex behaved on my home computer, I will get to test an Intel x25-e at their place. That's the second time when I invested in my computer at home it helped me in my career. The first time was getting an AMD 64 bit system before most companies had it and using it at home with Linux and MySQL. The ex complained it was a waste of money, but it was a hell of an impressive thing to say at the time during interviews that I had 64 bit Linux and MySQL running at home, and it proved to be true. If you get a good raise because you show initiative when investing money into your home equipment to prove something, it pays for itself.

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Mark leads the Ubuntu California Team. You can reach him at ubuntu.ca.team@gmail.com .