Do you need to 'eject' USB HDD? Do they auto park at power-off?

[Coffeegeek]

Hi,

We are using two USB hard drives (250gb) as backup for our companies
system. Each is used to contain a complete image of the entire server,
and is swapped over every night with the other.

There is a power switch on the housing, which we have been turning
off, then disconnecting the drive, connect the new one, then turn it's
switch on.

Does anyone know if turning off with this switch will let the drive
park it's heads, or should we still go through the full 'eject'
hardware (soft switch) route?

I look forward to your replies.

Thanks in advance,

Coffeegeek

 

[Arno Wagner]

Hi,

We are using two USB hard drives (250gb) as backup for our companies
system. Each is used to contain a complete image of the entire server,
and is swapped over every night with the other.

There is a power switch on the housing, which we have been turning
off, then disconnecting the drive, connect the new one, then turn it's
switch on.

Does anyone know if turning off with this switch will let the drive
park it's heads, or should we still go through the full 'eject'
hardware (soft switch) route?

I look forward to your replies.

Thanks in advance,

Coffeegeek

The head-parking is not an issue. The drive can secure its hardware
on unexpected power loss without problems.

What could be an issue is that the OS might not have flushed its data
to disk from internal buffers, leaving you with an unusable
backup. Typically it works, since, if the system is idle, even
non-server OSes like the ones Microsoft makes, flush to disk within
seconds. Under load a flush can be delayed up to 5 Minutes (typically)
and can then take up to 3 hours for 250GB with the typical USB speed
of 25MB/s. So if you remove the disk while it is still being written
to or the server is busy with some other disk operations and has not
yet written everything to disk, you will get data loss.

The only way to be really sure the data is on disk is to use
the OSes drive removal function ("remove hardware safely" under
Windows, "umount" under practically every Unix) and to wait until
it has completed.

Arno

 

[Eric Gisin]

We are using two USB hard drives (250gb) as backup for our companies
system. Each is used to contain a complete image of the entire server,
and is swapped over every night with the other.

There is a power switch on the housing, which we have been turning
off, then disconnecting the drive, connect the new one, then turn it's
switch on.

Doesn't matter what order you do this.

Does anyone know if turning off with this switch will let the drive
park it's heads, or should we still go through the full 'eject'
hardware (soft switch) route?

There is no need for this, all drives autopark.

You do need to tell the OS you are removing a drive.
In Windows, simply use "safely remove drive".
This flushes the OS and drive's cache.

 

[Kwyjibo]

The head-parking is not an issue. The drive can secure its hardware
on unexpected power loss without problems.

What could be an issue is that the OS might not have flushed its data
to disk from internal buffers, leaving you with an unusable
backup. Typically it works, since, if the system is idle, even
non-server OSes like the ones Microsoft makes, flush to disk within
seconds. Under load a flush can be delayed up to 5 Minutes (typically)
and can then take up to 3 hours for 250GB with the typical USB speed
of 25MB/s. So if you remove the disk while it is still being written
to or the server is busy with some other disk operations and has not
yet written everything to disk, you will get data loss.

By default,Windows XP and Vista disables write caching on any drive it
recognises as 'removable' so that should not be an issue.
Have a look at the drive properties in device manager and you will see that
caching is disabled.

 

[Arno Wagner]

By default,Windows XP and Vista disables write caching on any drive it
recognises as 'removable' so that should not be an issue.

Unless a write is still in progress. This may not even show
up as activity on the drive, when the writing programm stops
at the moment, e.g. because of waiting for other disk activity.
The only way to make sure is to "safely remove".

Have a look at the drive properties in device manager and you will
see that caching is disabled.

It can be activated. So there is an assumption about a non-obvious
property to be still in the default setting. Dangerous. In a
professional neglient.

Arno

 

[John Turco]

Doesn't matter what order you do this.

There is no need for this, all drives autopark.

You do need to tell the OS you are removing a drive.
In Windows, simply use "safely remove drive".
This flushes the OS and drive's cache.

Hello, Eric:

Is the "safely remove drive" procedure, an absolute requirement? Since
February, I've been solely using the enclosure's power switch, on my
SimpleTech "SimpleDrive" (160GB USB external hard disk). Thus far, I
haven't noticed any obvious ill effects -- yet, perhaps, there could
be more subtle ones?

Incidentally, I only employ the SimpleDrive, for daily backup purposes.

Thanks, for any advice!


Cordially,
John Turco <[email protected]>

 

[bealoid]

[snip]

Is the "safely remove drive" procedure, an absolute requirement?
Yes.

Since
February, I've been solely using the enclosure's power switch, on my
SimpleTech "SimpleDrive" (160GB USB external hard disk). Thus far, I
haven't noticed any obvious ill effects -- yet, perhaps, there could
be more subtle ones?

You'd notice pretty soon - Windows will pop up a message saying a drive was
removed improperly and data has been lost.

 

[Arno Wagner]

Hello, Eric:

Is the "safely remove drive" procedure, an absolute requirement? Since
February, I've been solely using the enclosure's power switch, on my
SimpleTech "SimpleDrive" (160GB USB external hard disk). Thus far, I
haven't noticed any obvious ill effects -- yet, perhaps, there could
be more subtle ones?

Incidentally, I only employ the SimpleDrive, for daily backup purposes.

Thanks, for any advice!

It is the only safe thing to do. True, for many usage patterns,
not doing it may work well and only very seldomly lead to data
corruption. But it allways can. If you "safely remove", you will
not get corruption and you data will be on disk.

Arno

 

[Kwyjibo]

Unless a write is still in progress.

Read it again.
I said 'write caching' should not be an issue as it is disabled.
If a write is in progess but caching is disabled I agree that it could cause
problems, but those problems have absolutely nothing to do with write
caching.

If you are going to bother replying, please try to ensure that your post is
factually accurate.

 

[Arno Wagner]

Read it again.
I said 'write caching' should not be an issue as it is disabled.
If a write is in progess but caching is disabled I agree that it could cause
problems, but those problems have absolutely nothing to do with write
caching.

And neither did I claim it does. There are two problems here.
Open files by an application and write-caching by the OS. To
nit-pick, the application itself could also do some form of
write-caching, although that is rather rare.

If you are going to bother replying, please try to ensure that your
post is factually accurate.

I did. Maybe you should read my posting again?

Arno

 

[John Turco]

[snip]

Is the "safely remove drive" procedure, an absolute requirement?
Yes.

Since
February, I've been solely using the enclosure's power switch, on my
SimpleTech "SimpleDrive" (160GB USB external hard disk). Thus far, I
haven't noticed any obvious ill effects -- yet, perhaps, there could
be more subtle ones?

You'd notice pretty soon - Windows will pop up a message saying a drive wasmy computer.
removed improperly and data has been lost.

Hello, Bealoid:

Thank you; I was mistaken, though. I don't turn on the SimpleDrive,
till I need to copy files to it. Then, I shut it off, >after< closing
down my computer.

I don't want to leave it running, too long, as I fear that heat may
shorten its life. (Its enclosure lacks a fan.)

Sorry, for any confusion!


Cordially,
John Turco <[email protected]>

 

[John Turco]

Arno Wagner wrote:

It is the only safe thing to do. True, for many usage patterns,
not doing it may work well and only very seldomly lead to data
corruption. But it allways can. If you "safely remove", you will
not get corruption and you data will be on disk.

Arno

Hello, Arno:

Thanks. See my previous reply (to "bealoid"), for further explanation.


Cordially,
John Turco <[email protected]>