# Individual disk access on RAID 1

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Is there a way to circumvent the fact that on a RAID 1 (mirroring) system a pair of hard drives are seen as one and, when writing a file, override the default "write in parallel mode" behaviour and instead write in a weird kind of striping mode by interleaving the written segments in the following way:
[start write]

[write]
HDD1  ----    ----    --
HDD2      ----    ----

[end write]

[synchronize]

When writing is finished, free up control from the output process, but spawn a background sychronization thread that copies the missing portions to the complementing hard drive, maintaining the RAID 1 parallelism. This would allow increasing write speeds two-fold on RAID 1 systems during periods when fast output to disk is the priority, but will require more time later on to do the synchronization. Could be very useful for some applications. I do realize that there are probably no ready means of accessing RAID 1 disks individually, especially if RAID is maintained in hardware; and if there is a way, it would most likely entail writing a device I/O driver. However, conceptually, this shouldn't bring about added risk if one of the drives fails while they are not synchronized since the only file that would be lost is the file that is being written.

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I'm not sure about writing but that is how data is read from RAID1 disks.

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Considering that hardware can make RAID invisible to the OS (though that is generally only enterprise-level hardware), I doubt very strongly that there is any way to do what you ask besides interfacing with the specific RAID hardware/software you're using.

Also, while that scheme doesn't greatly increase the risk of lost data, it would almost certainly increase the window that a file is vulnerable - don't forget both drives can write simultaneously and drives are very likely optimized for typical use (meaning sequetial reads and writes). Writing and reading every other sector/cluster/etc could completely invalidate all the asumptions the caching system makes.