yukondude's questions

I'm preparing a Dell R520 PowerEdge server with 8x 1TB disks as a data archive/warehouse (file, RDBMS, NoSQL) server. Out of the box, the PERC H710P RAID controller was configured with 3x 2TB RAID6 virtual disks. My understanding is that the 2TB limit is something to do with Windows "basic disks" (http://technet.microsoft.com/en-us/library/cc773268.aspx).

I'll be installing either Debian 7.4 or Ubuntu 12.04 LTS as the OS. For simplicity's sake I would like to create a ~5TB partition for data storage.

Is it advisable to create an LVM partition of that size that spans the three virtual disks? Does that lessen the effective 2-disk tolerance that I get from RAID6? Or are there performance issues when spanning LVM over multiple disks like that?

Or, would it be better to delete and recreate the virtual disks as one large 6TB RAID6 virtual disk? Is Debian or Ubuntu also limited to 2TB? I believe that used to be the case. Is it still?

Please Note: The problem I describe below seems to have "gone away" on its own. But that's not very comforting, so I'm hoping for a solution, or at least an explanation, should it recur.

I was just preparing a Slicehost virtual server for a LAMP role, using the Ubuntu Lucid server (CLI-only). I created an account for myself (yukondude) but was doing most of the installations as root. At some point in the process, the mysql-server package (aptitude install -Pr mysql-server) failed with this error:

Unable to set password for the MySQL "root" user

An error occurred while setting the password for the MySQL administrative user.
This may have happened because the account already has a password, or because of
a communication problem with the MySQL server.

This was the first time mysql-server had been installed, so the problem couldn't have been a previous password. The installation script then dumped these lines to the terminal:

100903 19:57:05 [Note] Plugin 'FEDERATED' is disabled.
/usr/sbin/mysqld: Can't create/write to file '/tmp/iblv4tJ0' (Errcode: 13)
100903 19:57:05  InnoDB: Error: unable to create temporary file; errno: 13
100903 19:57:05 [ERROR] Plugin 'InnoDB' init function returned error.
100903 19:57:05 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
ERROR: 1146  Table 'mysql.user' doesn't exist
100903 19:57:05 [ERROR] Aborting

It hung at this point, so I manually killed the installation processes.

I then discovered that the Apache2 server was refusing to serve my test index.html file, instead producing a 403 Forbidden message, even though the permissions for /var/www/index.html were wide open and the Apache config hadn't changed. I was also unable to log in through SSH to my yukondude account, and the command su - yukondude produced a cd /home/yukondude Permission Denied error (I'm afraid I don't have a copy of the exact error message). The permissions and ownership for /home/ and /home/yukondude/ were perfectly normal. Looking back at the mysql-server errors, I wondered if the access to the file in /tmp/ was related.

What could've caused this bizarre permissions problem? I've never seen anything like it before. I wondered whether PAM might be involved, but I don't know that system as well as I should. I'm not sure whether the mysql-server install was really the culprit, or just a victim of the permissions problem that cropped up at that moment.

I tried a complete re-install from a fresh image with the exact same result. My third and final attempt did work (the difference was that I updated my package versions before any installations), so I appear to be in the clear this morning. But I'm nervous that the same problem might someday re-occur. I tried Googling for help, but haven't figured out a good search phrase. Any suggestions?

Update: I'm going to start a bounty. As I pointed out, this problem isn't affecting me anymore, but I sure would like to have an inkling of what happened. I'd also appreciate comments from anyone who's experienced something similar in case those circumstances provide clues.

Our small community college assigns each of our approximately 1000 students a personal My Documents folder that is an alias for a Windows server share (also mapped as their P: drive). Students access this from their computer lab accounts. For security reasons, this share is not accessible from our wireless network segment, nor from the public Internet.

Naturally, students would like to access their college files from their laptops and from home. Can anyone recommend a reasonably secure web-based storage system (open source or commercial) that could serve their shares from the Windows file server (Active Directory-managed accounts)?

To make it as simple to use as possible, an ideal system would feature a client that could mount the connection to the web-based storage as a virtual filesystem. A lightweight or Flash client to support drag 'n drop and multiple-file up/download would be an acceptable alternative. Do either of these exist?

I especially welcome comments from anyone who's tried this, especially for a large, transient group of users that have wildly varying levels of computer literacy.

I recently wrote a complex SELECT statement (based on many very, very complex views) that would take 1 hour and 50 minutes to execute when run from Toad on my desktop, and only a few minutes faster when run from a Python script using the cx_Oracle library (written to flush to disk every 50 rows). The total size of the single result set was about 8000 rows totalling 5MB. During execution, my workstation was not thrashing and the CPU load was reasonably low.

The exact same query ran on the server took an astonishing 21 seconds to produce a byte-for-byte identical result set. This was also generated by the same Python/cx_Oracle script.

Transferring the 5MB result set file from the server to my workstation took only 3 seconds, so I don't think network bandwidth is the direct problem.

Could SQL*Net or one of its associated libraries be the culprit? Is there some non-linear memory management problems when queries are invoked across the network? A 5MB result set is large, but not ginormous in this day and age. Are there perhaps some buffer size configuration settings that would help? I'm using a vanilla Oracle client install.

The workstation is Windows XP Pro SP3 (only 1GB of RAM) with the Oracle 10g client and Toad for Oracle Xpert 9.7.2.5 and Python 2.6.2 with cx_Oracle 5.0.2. The server is Red Hat 2.6.9-67.ELsmp on a quad Xeon 3.8GHz 8GB server, running Oracle 10.2.0.4, Python 2.3.4, cx_Oracle 4.4.1.

Edit: Whoops! The file was only 5 Megabytes, not GB. Very sorry.

Solved: There was a population script that ran before the extract query that I mentioned. Once that population script was re-run, the extract query took 2 hours to run regardless of the location of the client program. After that first long run, the result set must've been cached somewhere, and I didn't notice that effect until I methodically went through all of the combinations.