Gentoo Archives: gentoo-user

From: Florian Philipp <lists@××××××××××××××××××.net>
To: gentoo-user@l.g.o
Subject: Re: [gentoo-user] {OT} SSD instead of RAID1?
Date: Mon, 27 Jul 2009 17:43:30
In Reply to: Re: [gentoo-user] {OT} SSD instead of RAID1? by Grant
1 Grant schrieb:
2 >>> ... What if I bought a low-price/low-capacity SSD drive for each
3 >>> of these systems, installed the system essentials on them, and used my
4 >>> existing high-capacity HD drives for data storage? Would each system
5 >>> keep running if the HDs died? If so, I think that would offer as good
6 >>> or better system reliability than RAID1. What do you think?
7 >> You don't need to buy SSD "drives" - instead you could use CF cards and a
8 >> cheap adaptor. These are commensurate in capacity & cost with USB flash
9 >> drives (4gig, maybe 16gig?), but CF cards "talk EIDE" and you can get cheap
10 >> pin-convertors allowing you to connect them to EIDE cables and treat them
11 >> like a hard-drive.
12 >
13 > Aren't CF cards much slower than SSD drives and HD drives?
14 >
16 Yep, especially the cheap ones which do not support DMA, just PIO. But
17 this is not necessarily a problem: After starting all services etc.
18 there will be very few reads on stuff like /etc and /usr. Just make sure
19 to put all directories to which you write (parts of /var like /var/log
20 and the several tmp directories) on an HDD, NFS or tmpfs. Of course,
21 this all depends on your usage patterns and how much RAM you have.
23 If you really need to write to the CFDisk, make sure to buy one with DMA
24 support (and no, the label "super fast" which is regularly found on
25 these things does not necessarily mean that it supports DMA).
27 One drawback of this configuration: You can never use swap - never!
28 Neither on the HDD (there is a high chance that the system would crash
29 when the HDD fails) nor on the (cheap) SSD/flash drive (the drive would
30 wear down, removing any advantage you tried to gain).
32 >> I know of these used in Asterisk based PABX systems & PoS tills with the
33 >> expectation that they're more reliable than disks, and have read statements
34 >> by people deploying quantities of such machines that they've never had a
35 >> failure in years of use.
36 >
37 > I like the sound of that.
39 Where I work, we have a System-on-a-Chip (SoC) NAS. Albeit being the
40 second most powerful machine we have in our server room (quad core CPU,
41 lots of RAM, three redundant power supplies and a good dozen HDDs), the
42 OSS itself resides on a removable card not bigger than my thumb.
44 >
45 >> I don't know how that really compares to RAID 1 - if you use hardware RAID
46 >> (and you can get hardware SATA controllers for £50 these days) then you can
47 >> assign a hot-spare, and hot-swap a replacement drive with zero downtime.
48 >> With hardware RAID you can still boot if one of the drives fails, but you do
49 >> add the controller as a potential point-of-failure.
50 >
51 > Would the system keeping running if I used a CF or SSD for the system
52 > install and the HD drive died?
53 >
54 > - Grant
55 >


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Subject Author
Re: [gentoo-user] {OT} SSD instead of RAID1? Florian Philipp <lists@××××××××××××××××××.net>
Re: [gentoo-user] {OT} SSD instead of RAID1? James Ausmus <james.ausmus@×××××.com>
Re: [gentoo-user] {OT} SSD instead of RAID1? Grant <emailgrant@×××××.com>
Re: [gentoo-user] {OT} SSD instead of RAID1? Nevynxxx <nevyn@××××××××××.uk>