Backup

[advix]

How long it will takes(approximately) to backup 86GB data to external 2.5"
hard drive (USB2.0)

 

[Tim Meddick]

Depends on different things such as; speed and resources of the computer,
efficiency of installed HDs and backup method & type of software employed.

But if you insist on an estimate, I would have said somewhere in the order
of about 2hrs.

==

Cheers, Tim Meddick, Peckham, London.

 

[Paul]

Depends on different things such as; speed and resources of the
computer, efficiency of installed HDs and backup method & type of
software employed.

But if you insist on an estimate, I would have said somewhere in the
order of about 2hrs.

==

Cheers, Tim Meddick, Peckham, London.

Since we're starting a betting pool, I take "1 hour if they're mostly movies"
and "5 hours if they're tiny files" If the backup software uses compression,
then it really isn't possible to make a guess. It'll be slower.

Paul

 

[advix]

Since we're starting a betting pool, I take "1 hour if they're mostly
movies"
and "5 hours if they're tiny files" If the backup software uses
compression,
then it really isn't possible to make a guess. It'll be slower.

Paul

 

[Paul]

There are no backup program, just copy files from hard drive to external
drive via USB2.0. Many small files, mostly.

When there are many tiny files, the head on the disk has to move around
a lot. Most of the time is spent moving the heads, very little time
transferring files. That's why the estimate varies so much. If the files
were all big ones, like movie files, then one hour would be enough. If
the files are tiny, then you're no longer looking at transfer rate
limitations. You're looking at the effects of head movements (hundreds
per second).

Think of it this way. About the worst performance you can get from
a disk, is when it's being defragmented. And when that is going on,
the disk gives 1MB/sec to 3MB/sec performance (varies a bit with the
OS being used). And then, you're talking about waiting a long long
time for it to finish. If the head is moving around continuously
like that, there is very little data transfered. You can't do much
worse than the defragmenter performance level. If we take 86000MB
divided by 1MB/sec, that would take 86000 seconds or pretty close
to 24 hours. My pick of five hours, is to account for not all of
the files being small ones, and a mix of small and large ones
improves the transfer rates a bit. If you had a pathologically
bad disk content, of only tiny files and purely tiny files,
it's going to take 24 hours to finish the transfer.

When transferring nothing but big movie files, the heads
don't have to randomly access at quite as high a rate, and
more of the time is spent transferring blocks of data. Then,
the USB bus is the limitation.

For example, when I back up my OS drive, and transfer the
pagefile or hiberfile (relatively large files), the transfer
rate is between 110 and 125MB/sec. Which is well above the
USB2 rate. If I was transferring to a USB enclosure, for those
two files, I would be limited to the ~30MB/sec of the USB2 bus.

This is from the log file of my last Robocopy run. From this,
I can see my average performance.

Speed : 39,240,045 Bytes/sec.

which if applied to your situation, taking the 30MB/sec limit
of the USB2 bus, would mean the USB2 bus is the limitation.
If you have a higher percentage of small files than I do, then
your time will be longer. I have 38973 MB for 177104 files, or
about 0.22MB per file average size. Work out your average size,
as a means to tell whether your backup is "better or worse"
characteristics than mine. The smaller your average size is
for the files, the lower the "Speed:" will be. Again, this
is only an estimate, not a precise prediction or anything.
I'm trying to find ways to guess at the answer.

Paul

 

[Tim Meddick]

What you are saying makes no sense! - All data is treated exactly the
same - no matter what type of file it belongs to - when using imaging
software, the disk is continuously read and data copied at a consistent
rate of speed, only depending, as I said, on factors such as "speed and
resources of the computer, efficiency of installed HDs and backup method &
type of software employed".

==

Cheers, Tim Meddick, Peckham, London.

 

[Paul]

What you are saying makes no sense! - All data is treated exactly the
same - no matter what type of file it belongs to - when using imaging
software, the disk is continuously read and data copied at a consistent
rate of speed, only depending, as I said, on factors such as "speed and
resources of the computer, efficiency of installed HDs and backup method
& type of software employed".

==

Cheers, Tim Meddick, Peckham, London.

Say, on average, it takes 10 milliseconds to move the head from one part
of the disk to another. When the head is moving, no data can be transferred.
Data can only be transferred when the head is stationary over the cylinder
of interest.

If I'm transferring 2KB files, I do a 10 millisecond head movement, followed
by such a short transfer interval, the time for data transfer phase is very close
to zero. (The time is 0.002MB / (125MB/sec) = 16 microseconds.)

The relative percentage of the time that the disk is in data transfer phase, is
16 microseconds / (10 milliseconds plus 16 microseconds). 0.000016 / (0.010000 + 0.000016)
is 0.16 percent.

Now, if I'm working on big files, perhaps I spend 10 milliseconds to move
the head, then I get to transfer a 100MB chunk of contiguous sectors. To
move 100MB, at 125MB/sec sustained transfer rate, takes 0.8 seconds.

Now, the relative percentage of the time I'm transferring data is
0.8 seconds / (10 milliseconds plus 0.8 seconds) or 0.8/0.81 or getting
close to 100%. Now, I'm getting to use most of that sustained 125MB/sec
transfer rate the head-to-media is rated for.

To work an example, with the small file pattern, I can do around 100 head
movements of 10 milliseconds each, in a given second. I can then transfer
200 small 2KB files, for a total of 400KB in that second. And that gives
me 400KB/sec as a transfer rate. When the transfer pattern is dominated by the
time spent on head movement, very little gets done. This is the pattern you
see during disk defragmentation (which is why I mentioned 1MB/sec to around
3MB/sec - I've measured this with the Performance plugin, while the
defragmenter is running).

That's how I can estimate it will take one hour with movie files, and perhaps
five hours if all the files are much smaller.

If you don't believe me, get a copy of Robocopy, and copy one of your
partitions to another empty partition. Use the Performance plugin in Windows,
and add a counter to graph disk read bytes per second and disk write bytes per
second. When Robocopy is copying your pagefile, the graph will jump to an average
speed of 125MB/sec during the transfer of that file. (It'll take a few seconds
to complete the transfer.) When it hits one of your directories which contains
many small files, the transfer rate will plummet, because percentage-wise, in
a given second in that case, most of the time is spent pushing the head around
the platter and doing no useful transfer work.

HTH,
Paul

 

[Tim Meddick]

You are in error because disk-imaging software doesn't access or even
recognise separate "files".

Disk-imaging software, as I have said twice now, woks by copying the
partition or physical disk - sector by sector - not file by file... Files
don't enter the equation with disk-imaging.

==

Cheers, Tim Meddick, Peckham, London.

 

[Paul]

You are in error because disk-imaging software doesn't access or even
recognise separate "files".

Disk-imaging software, as I have said twice now, woks by copying the
partition or physical disk - sector by sector - not file by file...
Files don't enter the equation with disk-imaging.

==

Cheers, Tim Meddick, Peckham, London.

Timmy, read what the poster "advix" wrote:

"There are no backup program, just copy files from hard drive to
external drive via USB2.0. Many small files, mostly."

Now STFU!!! You moron. YOU MORON.

Paul (whose blood pressure has just hit the roof, and I'm out of here to cool off)

 

[Tim Meddick]

Please don't get emotional...

My comments about speed of backup were assuming the use of disk-imaging -
which is by far, the most popular method of backup today. Even brand new
PCs have ditched the accompanying setup cd-rom for the recovery partition -
a disk image!

I concede the OP did say "no backup program, just copy files" - but AFTER
you and I started our little side-conversation. Plus, in my initial
comments, I stated quite clearly that I was talking about disk -imaging
BEFORE your chapter and verse on "read-head movement".

==

Cheers, Tim Meddick, Peckham, London.

 

[Tim Meddick]

You should really consider using a disk-imaging program, it's much more
efficient and the backup times are allot quicker.

==

Cheers, Tim Meddick, Peckham, London.