Why initialize raid

Did you mean:. All forum topics Previous Topic Next Topic. Reply 1. Post Reply. Top Contributor. Dell Support Resources. Latest Solutions. Can't find what you're looking for? You can post your question in our community. Sign up now. I can see why periodic checks for readability of data can be useful. But what good does a periodic check for the replicas being identical do? Such checks can be useful if performed by a file system which checksums data.

But at the RAID layer without file system knowledge you cannot know which of the two different replicas is good, you cannot know how the discrepancy happened in the first place, and you cannot know which file if any is affected.

So it appears alerts about inconsistencies at this layer are mostly useless as there is nothing the administrator can do with the alerts anyway. As you need to read the data anyway, the cost of comparing it is minimal, but it can show you that one of the disks has developed an otherwise undetected problem e.

The administrator would then break up the array, manually look at the differences and choose which drive to replace. You should expand on that in your answer then. I know it's been many years, but this is the only valid reason I can see. I do not think it matters otherwise if the data is out of sync, as that data is by definition not written to yet, so the filesystem applied to the raid drive will never read from those blocks.

Making sure the periodic checks pass from the start, though, makes this necessary. The mdadm option --assume-clean does this, but warns you: --assume-clean Tell mdadm that the array pre-existed and is known to be clean.

But: a When doing mkfs some utilities check if there's something on that drive already. Why resyncing with RAID1 devices? Caveat: This is all undefined behavour.

Torinthiel Torinthiel 2 2 bronze badges. Please provide a citation for If you don't do it, there is a discrepancy between the drives and it's read, the RAID device will report failure of a drive. I believe that statement is incorrect.

At least provide an example of the error message such that it is possible to consult the source to verify under what circumstances it is produced. That's better. Did you verify the statement about writing zeros? I think it doesn't write zeros but rather copy one of the disks to the other s. In danger of what? I realize that the read may result in anything, but why would that result in some kind of danger for the user if a the information being read is not used anywhere and b a write is about to happen?

Test on on urandom -initialized device, with linux mdadm shows that first 80k remain different, as well as the last 48k. The latter probably due to rounding of RAID size to block size. Since you can use the disk while it is initializing, you may have written data at block , Once the raid init gets to that block, both A and B are already identical, so nothing happens. If It were instead zeroing blocks, it would wipe good data.

Thus, once again, I see two reasons to ensure the blocks are identical: "it's always been done" and "so you can run a check later" -- I also question that check's usefulness. Reading is good, comparing? Show 5 more comments. Michael Hampton Michael Hampton k 39 39 gold badges silver badges bronze badges. Comments are not for extended discussion; this conversation has been moved to chat.

They need to be turned into perfect copies of each other. HBruijn HBruijn But why do they need to be perfect copies of each other? What could possibly break from the two being inconsistent in sectors that were never used by the file system?

So the question becomes, what is the "file system" to which you refer. Taemyr I am not referring to any specific file system. Pick whichever you prefer and explain what would break by using it on a RAID-1 where the replicas were not in sync before initializing the file system.

Close Window. Such a disk change notification can be the result of hard drive failure, or one or two of the RAID drives going offline, depending on the RAID configuration. Before deciding to initialize the existing RAID array, please take a moment to consider the consequences. If you decide to initialize you will lose all existing data on the RAID array. It may be prudent to try other steps first to repair the failed array.

Check on the Tested Hardware and Operating System list which firmware the hard drive was validated with by Intel. If there is a different firmware version on your hard disk, check with the manufacturer, what the differences between these firmware versions are.

A newer drive firmware may support features which the SSE does not support. Such features may be enabled by default on the drives. If that is the case, the drive manufacturer may be able to provide tools to turn such features off.