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Software RAID problems

My friend and colleague Tom Bridge sent me a useful bit of information for those interested in the Mac Mini Server...

"Mirrored Apple RAID and SoftRAID cause kernel panics under 10.6 and 10.6.1 server."

What this means is that the Mac Mini Server is not really all that useful until they resolve this issue, and anyone updating their software RAID-based servers should hold off as well.

Further research indicates that some people feel that it has to do with custom block sizes. I was unable to ask Tom whether his experience with this bug was the result of custom block sizes or not, although I doubt he would have done so.

This probably affects Snow Leopard client as well.

Mac Mini Server

Last Tuesday, Apple released a Mac Mini that has Mac OS X Server preinstalled. Fitted with two 500 GB drives, 4 GB of RAM, and a 2.53 GHz Core 2 Duo processor, it is a nice little device for providing services to a small office, whether it be a Mac or Windows-based business.

Why do I say that it is a good server for Windows networks? Look at the "starter" Dell, pulled at time of post from their website.

$1059 - 1x250GB hard drive, 4 GB of RAM, 2.8 GHz Core 2 Duo processor and no operating system.

+ $150 to upgrade the hard drive to 500 GB

+ $150 to upgrade the second hard drive to 500GB

+ $399 for Red Hat Enterprise Linux

So for $1758, a business can either purchase an "entry level" Linux-based server or a Mac Mini-based server with an extra 2.7 TB external RAID5 array ($799.) If you want to use a Windows-based operating system, you need to add another $1100 to that price.

In summary, the Mac Mini server is not an enterprise-level server, capable of supporting hundreds of users. However, it is most likely a perfect fit for most small businesses and entrepreneurs.

Backups

This was originally published on the Des Moines MUG mailing list, where it was suggested that it be published.

The fiasco with the Sidekick phones provides the opportunity to talk about backups a bit...

1) A good backup is a verifiable backup.

If you are dumping info into Time Machine, and you are never pulling info back out of it and checking, how do you know that the data is good? In the instance of the SideKick data, this means that they would have known that the backup is good, and that they could rely on it. Until you know that you can recover from it, you cannot call it a good backup.

Spot checks of the data should be as important as the actual backup itself.

2) A good backup consists of many backups of the same data.

At my current job, I store three months of backups, and I consider that too little, but don't dare increase my budget. They are located both on-site and off-site, although they are only separated by about three miles, meaning there are several scenarios that could cause data loss.

- What happens if you are relying on all of your data being on a single hard drive, and there is a fire that destroys both your computer and backup?

- What happens if all of your backup is in one online cloud, and that cloud bursts like the SideKick cloud did?

If you have daily backups on a time machine volume, and a weekly backup to an online service, you are protected from either scenario. In this third scenario, the Time Machine backup is your primary, saving the changes that you make often. The online service is then your offsite backup, protecting you from physical destruction of the time machine and the computer at the same time.

If your backup strategy has any one point of failure, you need to reassess.

3) Synchronization is not backup.

Synchronization ensures that all of your data is the same between all instances that you create. If you are syncing your address book on your mac with an iPhone, you have two instances of the data, but they are tied together. If you delete a contact on one (or a virus deletes all of them) that deletion is transferred to your backup.

I realize that there are ways that the sync service tries to reduce the chance of this, but data loss is still a possibility. However, an offline copy of your address book on a USB thumb drive that is not plugged into your computer cannot not be changed, at least until it is plugged in again.

Furthermore, file corruption is not protected at all with Syncronization. Chances are, your corrupt file will appear more current than the good copies, and overwrite all of the good copies, usually just before you realize you don't want to sync them.

Dropbox is a synchronization service, meaning that it makes sure that two different folders, on two different computers contain the same information. However, Dropbox also has a backup service integrated into it as well; which saves your files in DropBox's cloud. There is a distinct possibility that DropBox could behave in the same way as the SideKick fiasco if their cloud were to burst, causing all of your files to sync with the now-empty file store on the cloud.

The way I use Synchronization Services is that I use it to ensure that all of the data is on our SAN, which is then backed up using normal backup procedures, this way, there is always an offline copy of the users' data.

4) RAID is not backup.

RAID (except 0) is a way to protect from hard drive crashes. It does not protect against application corruption, accidental deletion, or intentional deletion. All of which are much more likely than hard drive corruption during the majority of the life of a hard drive. RAID is useful for server admins who deal with distributing data amongst many hard drives, which actually is a great way to exponentially increase the likelihood of data loss due to hard drive failure.

RAID 0 offers no protection at all- in fact, it is will exponentially increase your likelihood of data loss due to hard drive failure. Be careful when purchasing large external hard drives, as they are sometimes two drives that are internally configured as RAID 0. This is useful for professional video primarily.

5) Backup as sparse as you are willing to recover from.

- If you couldn't stand losing more than a week's worth of data, you'd best be backing up weekly.

- If you couldn't stand losing more than a day's worth of data, you'd best be backing up daily.

- If you couldn't stand losing more than an hour's worth of data, you'd best be backing up hourly.

You know what is important and what is not. Make sure to tailor your backup routine to your needs. Incremental backups, such as Time Machine are good about this.

6) Recovery options are available, but expensive.

Data recovery costs a minimum of $1000 for a hard drive. And they don't guarantee they can recover anything. If you need such a service, please contact me and I can arrange for a discount with DriveSavers.