Re: [patch] document flash/RAID dangers

From: Pavel Machek
Date: Tue Aug 25 2009 - 20:44:46 EST

>>>> THESE devices have the property of potentially corrupting blocks being
>>>> written at the time of the power failure,
>>> this is true of all devices
>> Actually I don't think so. I believe SATA disks do not corrupt even
>> the sector they are writing to -- they just have big enough
>> capacitors. And yes I believe ext3 depends on that.
> Pavel, no S-ATA drive has capacitors to hold up during a power failure
> (or even enough power to destage their write cache). I know this from
> direct, personal knowledge having built RAID boxes at EMC for years. In
> fact, almost all RAID boxes require that the write cache be hardwired to
> off when used in their arrays.

I never claimed they have enough power to flush entire cache -- read
the paragraph again. I do believe the disks have enough capacitors to
finish writing single sector, and I do believe ext3 depends on that.

(cesky, pictures)
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