Re: [gentoo-user] {OT} SSD instead of RAID1?

[Grant <emailgrant@gmail.com>]

>>>> ... What if I bought a low-price/low-capacity SSD drive for each
>>>> of these systems, installed the system essentials on them, and used my
>>>> existing high-capacity HD drives for data storage?  Would each system
>>>> keep running if the HDs died?  If so, I think that would offer as good
>>>> or better system reliability than RAID1.  What do you think?
>>> You don't need to buy SSD "drives" - instead you could use CF cards and a
>>> cheap adaptor. These are commensurate in capacity & cost with USB flash
>>> drives (4gig, maybe 16gig?), but CF cards "talk EIDE" and you can get cheap
>>> pin-convertors allowing you to connect them to EIDE cables and treat them
>>> like a hard-drive.
>>
>> Aren't CF cards much slower than SSD drives and HD drives?
>>
>
> Yep, especially the cheap ones which do not support DMA, just PIO. But
> this is not necessarily a problem: After starting all services etc.
> there will be very few reads on stuff like /etc and /usr. Just make sure
> to put all directories to which you write (parts of /var like /var/log
> and the several tmp directories) on an HDD, NFS or tmpfs. Of course,
> this all depends on your usage patterns and how much RAM you have.
>
> If you really need to write to the CFDisk, make sure to buy one with DMA
> support (and no, the label "super fast" which is regularly found on
> these things does not necessarily mean that it supports DMA).
>
> One drawback of this configuration: You can never use swap - never!
> Neither on the HDD (there is a high chance that the system would crash
> when the HDD fails) nor on the (cheap) SSD/flash drive (the drive would
> wear down, removing any advantage you tried to gain).
>
>>> I know of these used in Asterisk based PABX systems & PoS tills with the
>>> expectation that they're more reliable than disks, and have read statements
>>> by people deploying quantities of such machines that they've never had a
>>> failure in years of use.
>>
>> I like the sound of that.
>
> Where I work, we have a System-on-a-Chip (SoC) NAS. Albeit being the
> second most powerful machine we have in our server room (quad core CPU,
> lots of RAM, three redundant power supplies and a good dozen HDDs), the
> OSS itself resides on a removable card not bigger than my thumb.

Is cost-savings the advantage of using CF instead of SSD?  It sounds
like it might be wiser to spend a little more (low capacity SSD drives
are pretty cheap now) and have a real storage device that doesn't need
an adapter and is much faster, can swap, etc.

I bet I'm missing something though...?

- Grant


>>> I don't know how that really compares to RAID 1 - if you use hardware RAID
>>> (and you can get hardware SATA controllers for £50 these days) then you can
>>> assign a hot-spare, and hot-swap a replacement drive with zero downtime.
>>> With hardware RAID you can still boot if one of the drives fails, but you do
>>> add the controller as a potential point-of-failure.
>>
>> Would the system keeping running if I used a CF or SSD for the system
>> install and the HD drive died?
>>
>> - Grant