Booting from a SW RAID

In the previous post I said that you cannot boot from the software RAID array. In fact, this is not true. All the widespread bootloaders, from Windows NT, Linux LILO, and GRUB, would successfully load OS from a RAID 1 (mirror volume).
It should be noted that some further actions must be undertaken for RAID 1 boot volume when you plan to build a RAID.

Since the mirroring technique does not extend to the Master Boot Record (MBR), you must copy the MBR manually between drives in a software mirror. Otherwise, once the primary (boot) drive fails, you will end up with an unbootable system.

Surely, there will be no irreversible data loss - all you need is to just mount the disk into some other machine and read it, but you get no automatic recovery in case the disk fails in operation, requiring a reboot.

Make a software RAID bootable?

Is it possible to create a bootable software RAID0, RAID 5, or spanned volume containing a Windows installation?
Unfortunately, no. It is not possible to boot from a software RAID0, RAID5, or spanned volume. A hardware RAID controller is required to do this.

You cannot start an OS from the software RAID because the RAID is not accessible until the OS is fully started up, and the operating system itself is on the array.

Why it is critical to read data off both disks in RAID1?

When using RAID 1 it is needed to access data stored on the second member disk as well. Otherwise it may lead to that a bad sector appears on the second member disk. In this situation the RAID 1 doesn't have redundancy any longer and on top of that you do not know it. Absolutely the same is true for hot spare drives.

Typically one of the causes of this issue is the array being idle. To avoid this situation you can inspect both copies of data while reading. It should be noted that heavily loaded RAIDs do not have such issue.

In Windows, at least up to Windows 2003, RAID1 software implementation usually reads from the first drive, rendering RAID 1 unreliable.

NAS and backup power

Just cutting off the power is not sufficient to test an UPS. Generally, Network Attached Storage receives the messages from its UPS unit constantly and reacts at once. It should be noted that during the start up the notifications about power problems are not received. Additionally, one should take into account that the entire cycle (start up then shut down) may require several minutes.
 Consider the following situation:

1. power failure happens
2. NAS takes power from the UPS battery for some time and then shuts down
3. the grid power turns on and the Network Attached Storage powers up and begins to start up
4. here power is off again.

Now NAS cannot process a report about power failure event until it properly starts up. Once NAS loads, it finds out that the power failure has happened and commands to shut down. Further it may happen that UPS is not able to provide power long enough (to shut down NAS correctly) for the battery is already exhausted during the first cycle.
 One can avoid this by setting the NAS up so that it shuts down as soon as it gets a message that power failure happens.

 All this allows saving battery charge to do one more cycle.

 Alternatively you can try to set Network Attached Storage up in such a way that it does not power up automatically, but per operator's command after the power failure has happened.

Benchmark software I tested

I wanted to test my data storage devices in terms of performance and so used three benchmark utilities:

• HD Tune Pro
• Crystal Disk Mark
• BenchMe

With HD Tune Pro I managed to get quite a number of diverse parameters, however, I'm sure that only linear read speed and average disk access time are of interest. Additionally, it was difficult to find such a basic performance parameter as I/O operations per second.

As for CrystalDiskMark, it cannot benchmark a physical storage, but is limited to partitions only. In my opinion this might be a drawback. It gives read/write speed for different number and size of queries. It is also possible to get benchmark both for linear and random read/write speed. This benchmark tool is designed so that user is able to change amount of data which is required to read during tests.

As for another benchmark tool BenchMe, it is a simple to use tool to benchmark storage devices. Unlike CrystalDiskMark, BenchMe handles physical devices, but not volumes. Using this tool one can obtain the following performance characteristics: linear read speed, distribution of disk access time, and a list of device capabilities. IOPS are measured for queue depth 1 and 32.

BenchMe and CrystalDiskMark are free programs, but when it comes to interface and graphical representation of obtained benchmark data, BenchMe has the best of both paid HD Tune Pro and free CrystalDiskMark.

How to use hot spare disks properly?

Nowadays, many storage systems utilize a hot spare disk which is dedicated to save your ass if a disk fails. But a few people really understand how to handle hotspare disks correctly - these disks required to be checked periodically.
Let's consider such a situation - you create your own RAID and put N drives (along with the hotspare disk) to the array. In this case there exists 1/N probability that exactly hotspare disk will be the first to fail. So now you no longer have a hot spare.
 When one of the RAID member disks fails you are surprised to learn that the hot spare disk already failed.
To avoid this you need to check a hotspare periodically or stick to RAID6E or RAID 5E/EE layout.

Wiping the hard disk at home

The drive which you are going to sell or dispose of may still contain either some personal data. This data is to be removed off the disk before getting rid of it.

As far as software is concerned, there are several programs both free and paid that can overwrite the  information by either 0s or random noise. Once overwritten, the data is irreversibly deleted.

To obtain the same result yourself as with the secure erase software, just format the hard disk and load it fully with some stuff you don't care about (similar to multiple copies of House MD videos). Once the big file fits no more, continue adding smaller files. You can also do this with an USB box. On modern full encryption disks, just changing a password gets you the same result as after a secure erase.