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Showing posts from January, 2011

How to enable root login in Ubuntu

Open terminal, type sudo passwd root, then enter the current password, then twice a new root password.
System reports back password updated successfully. Good.

Unfortunately, I did not figure out autologin.

Partition alignment

You can only align a partition (on a hardware block boundary) if a cluster size is an integral multiple of your hardware block size. This means you cannot align a HFS partition, because it would happily use 19 or 27 sectors per cluster. Most other filesystems would use a cluster size that is a power of two, matching the hardware block size.

Another thing is that if the boot sector and the data area use different alignments, it is the data area that you align. On FAT, there may be 1025 or whatever odd number of sectors between the boot sector and the first cluster of actual data. If you align the FAT partition's boot sector, the data would then be offset by one sector.

Multiple cluster sizes on a single volume?

it's been 10 years and I've yet to hear of a filesystem that uses multiple cluster sizes on the same volume. Otoh, I don't see what benefit that could possibly give.

With multiple cluster sizes on the same volume, you can do tailpacking.

Ext-series filesystems had a different block and fragment size, but never actually used it. Quite possible that was removed in ext4, although I'm not really sure.

OLE Structured Storage actually uses two different block sizes (small block and big block).

The coincidences

The Skype website was slow to load today. Went to tweet about that only to find that "Twitter is over capacity". Kind of ironic.

Is RAID5 faster?

Is RAID5 faster than a single disk?

On reads, yes.
On writes, sometimes.
On random writes, no.

Check the RAID Calculator if you need similar data on RAID 0 or RAID 6.

MBR/Boot in RAID

Which drive in a RAID stripe contains the MBR?

The first drive.

Bonus:

Which drive in a RAID stripe contains the boot sector?

On a hardware RAID, no specific location.
On a software RAID, the first drive.

RAID5:
In RAID5, if there are mostly zeros at the start of the volume, the parity block may contain an exact duplicate of the MBR/boot sector.

For other parameters, check RAID 0 Recovery primer.

RAID is for servers only?

Not true.

As long as you do backups properly, you can use RAID on workstations (HTPCs, DIY servers, whatever) as you see fit. Depending on what RAID type you choose, it gives you a performance boost, more capacity, or some added convenience, or all of this at once.

If you do not do backups properly, it does not really matter if you use RAID or not. Someday, you would evaluate our data recovery software. While it is rather good, admittedly not all cases of data loss are recoverable.

Mixing disks in RAID

Can I use one 10,000 RPM and one 7200 PRM hard drives in RAID 1?

Yes. In RAID1, that would not cause any noticeable issues.

Incompatibilites

Got a DVD burner under Vista that would eject the drive if the card reader with a memory card in it is plugged into the USB port. The burner is internal (SATA). The disc would not stay in (gets ejected after about five seconds) until the card reader is disconnected. Go figure.

What they don’t tell you about all the new technology

Some new technologies have side effects which decrease data redundancy. Such technologies are:
NTFS compressionWindows Vista/7 vs. Windows NT/2000/XP complete formatTRIM on SSDsZFS deduplicationInitially, the effect of decreasing redundancy is unnoticeable, but once the technology becomes popular, the unintended consequences appear.
Volume-level NTFS compression never became widespread among home users.As Windows Vista and then Windows 7 become widespread, the number of cases when data is lost irreversibly due to reinstallation increased. You can recover some data after XP reinstallation, but not after Vista/7 reinstallation with a complete format.SSDs with TRIM are not widespread enough (yet) to notice that data recovery software does not properly work with them. As for ZFS-based NASes, then on the one hand they are not widespread among the home users, on the other hand - even the first installations did not yet reach the end of their service life.

Deduplication

Data recovery software is based on the filesystem and user data redundancy.

In case of significant filesystem damage user data redundancy is often required for data recovery software. Elimination of user data redundancy using a compression (as in NTFS) or a deduplication (as in ZFS) complicates automatic data recovery.