RAID disk replacement

  • Thread starter Thread starter Jake Lee
  • Start date Start date
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Jake Lee

Generally speaking, in a RAID setup, if a single drive fails it would seem
ideal to replace it with the exact same make/model drive if possible.
However, if this is not possible due to the age and lack of availability of
the failed drive, is it certain that the drive can replaced by a different
make/model one, so long as both the speed and the capacity are equal to or
greater than the original?

i.e. I could replace a 7,200 RPM 36GB drive with a 10,000 RPM 36GB drive
with no (apparent) problem? I wouldn't expect any performance gains from
having a single drive faster than the others...data integrity is the single
concern for my question.

I'm currently faced with this problem, and I'm getting some conflicting
info about the exact criteria required of the replacement drive in a RAID
system :(

That being the case, I'd especially like to hear from someone(s) who has
done this successfully in actual practice,...thanks!
 
Jake said:
Generally speaking, in a RAID setup, if a single drive fails it would seem
ideal to replace it with the exact same make/model drive if possible.
However, if this is not possible due to the age and lack of availability
of the failed drive, is it certain that the drive can replaced by a
different make/model one, so long as both the speed and the capacity are
equal to or greater than the original?
Click to expand...

I wouldn't go so far as to say it was _certain_ because sure as I do you're
going to find that you have some pathological combination of hardware and
software that won't allow it.

That said, I've never had any trouble replacing a member of a RAID
(hardware, software, ATA, SCSI, ESDI, or MFM) with a larger drive--the only
real rules I've found are that the new drive has to have the correct
interface, has to be compatible with whatever software and hardware you're
using, and has to have the same or greater capacity than the one it
replaces.
 
I wouldn't go so far as to say it was _certain_ because sure as I do you're
going to find that you have some pathological combination of hardware and
software that won't allow it.

That said, I've never had any trouble replacing a member of a RAID
(hardware, software, ATA, SCSI, ESDI, or MFM) with a larger drive--the only
real rules I've found are that the new drive has to have the correct
interface, has to be compatible with whatever software and hardware you're
using, and has to have the same or greater capacity than the one it
replaces.
Click to expand...

That matches exactly with what I've found. Also makes
for a slow-n-steady way to end up with a larger array
(once you've replaced the last small drive with a bigger
drive, backup-and-reinstall to take advantage of the
larger drives).

The other rule-of-thumb that I've heard when buying
initial drives for an array is to match the make-model
as close as possible. But make sure all of the drives
come from different manufacturing batches. (e.g. buy 1
here, 1 there, 1 from somewhere else, etc.) The idea
being that if there is a fatal flaw in a particular
batch, you won't have multiple drives fail at the same
time.
 
Toshi1873 said:
That matches exactly with what I've found. Also makes
for a slow-n-steady way to end up with a larger array
(once you've replaced the last small drive with a bigger
drive, backup-and-reinstall to take advantage of the
larger drives).
Click to expand...

Well in RAID 0 or RAID 1 then you are limited to the size of the smallest
drive.
 
Previously Jake Lee said:
Generally speaking, in a RAID setup, if a single drive fails it would seem
ideal to replace it with the exact same make/model drive if possible.
However, if this is not possible due to the age and lack of availability of
the failed drive, is it certain that the drive can replaced by a different
make/model one, so long as both the speed and the capacity are equal to or
greater than the original?
Click to expand...

Yes. But take care that it is really the same capacity or larger,
i.e. has at least the same number of sectors.
i.e. I could replace a 7,200 RPM 36GB drive with a 10,000 RPM 36GB drive
with no (apparent) problem? I wouldn't expect any performance gains from
having a single drive faster than the others...data integrity is the single
concern for my question.
Click to expand...

As long as the new disk is really larger. Exact disk sizes may differ
between models/manufacturers by some tens of MBs or more. If the
new disk is just one sector smaller, things may not work.
I'm currently faced with this problem, and I'm getting some conflicting
info about the exact criteria required of the replacement drive in a RAID
system :(
Click to expand...
That being the case, I'd especially like to hear from someone(s) who has
done this successfully in actual practice,...thanks!
Click to expand...

Only for software-RAID under Linux. The only limitation is the drive
size there.

Arno
 
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