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What is right SSD size to use for O/S in new PC build

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November 27, 2010 3:03:20 AM

Building a pc using SSD... what is the correct SSD size to use for the O/S and should I raid with a 2nd SSD (e.g., OCZ Vertex 2 OCZSSD2-2VTXE120G 2.5" 120GB SATA II MLC Internal SSD)? Also, if I should raid them, should I raid 2 Hard Drives (e.g., 1 TB WD Caviar Black 7200rpm) and which type of raid should I use: striped or mirror?

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a b G Storage
November 27, 2010 4:02:32 AM

Wow. There are as many answers to this question as there are users on Tom's. 30GB is enough for many. 120GB is too small for others.

Should I raid? NO. Buy an ssd that meets your needs. Leave RAID to your nas.

A striped raid will theoretically double the read/write speed of a drive whilst having a small negative impact on seek times.

A mirrored raid will give you redundancy so you can survive a drive failure without loss. Write time takes a BIG hit read and seek times basically unchanged.

If you have adequate storage you do not need a large ssd for os. If you plan to use the ssd for lots of video editing or some hard drive intensive tasks you may want to increase the size accordingly. If you're a gamer... the ssd may not help much with game play. Only load times. Certainly it will help your OS boot and response times.
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a b G Storage
November 27, 2010 4:20:11 PM

If you only install some basic applications (Office tools, anti-virus, IM, ...) along with your OS, a 40-60 GB is probably enough; just make sure your "My documents" and "Downloads" folders don't get too full or move them to another drive. My current OS drive is only 20GB full and I have Windows 7 Pro x64 along with Office 2003 installed there (plus other small crap).
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a c 179 G Storage
November 27, 2010 4:21:27 PM

1) Larger SSD's perform better than smaller ones. That is because internally, they can access more of the nand storage chips concurrently. Sort of an internal raid-0. No need for raid of ssd devices. Also, raid controllers currently do not pass the trim command to the ssd. That will cause ssd performance to degrade as the ssd gets filled. In order for windows-7 to transmit the trim command, the sata mode in the bios must be set to AHCI(not IDE, or RAID).

2) Windows 7 will take about 13gb withought any attemp to reduce it's size.

3) raid-0,aka striping, is helpful for large block sequential operations, not much else. The OS does mostly small random operations.

4) raid-1 duplicates data on two different drives. The value of raid-1 and it's variants like raid-5 for protecting data is that you can recover from a hard drive failure quickly.
It is for servers that can't afford any down time.
Recovery from a hard drive failure is just moments.
Fortunately hard drives do not fail often.
Mean time to failure is claimed to be on the order of 1,000,000 hours.(100 years)
Raid-1 does not protect you from other types of losses such as viruses,
software errors,raid controller failure, operator error, or fire...etc.
For that, you need EXTERNAL backup.
If you have external backup, and can afford some recovery time, then you don't need raid-1.
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November 28, 2010 2:21:37 PM

geofelt said:
1) Larger SSD's perform better than smaller ones. That is because internally, they can access more of the nand storage chips concurrently.


Is this true for the 60 GB Vertex 2 as well, or just for smaller drives? Does it depend on the controller?

Can you link to a review that explains the issue, or has a benchmark showing the effect, between say 60GB and 120GB Vertex 2, and/or the competition?
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a c 179 G Storage
November 28, 2010 3:36:26 PM

varis said:
Is this true for the 60 GB Vertex 2 as well, or just for smaller drives? Does it depend on the controller?

Can you link to a review that explains the issue, or has a benchmark showing the effect, between say 60GB and 120GB Vertex 2, and/or the competition?


The difference shows up in sequential operations more than random. Raid-0 also shows up better than random, so there are two ways to go about getting better sequential speeds. Look at two different sized SSD's in the anandtech ssd bench table:
http://www.anandtech.com/bench/Product/126?vs=125
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November 28, 2010 3:49:48 PM

Comparing 40GB Sandforce (Corsair Force series) to 120GB of the same model is perhaps better as it shows the contrast better. Still a lot of benchmarks aren't that different, less than 15%. If the difference isn't higher, then it could be best to just buy small SSDs frequently, as each generation will probably bring improvements of 50% or more, in terms of performance, capacity and/or price.

http://www.anandtech.com/bench/Product/196?vs=195

There are some benches which have a much higher difference though - in this link, the ATech storage bench (both light and heavy version). Also the 4KB random read, where the difference is huge - I suspect the benchmark is the one having a problem and the result is not valid, how else could there be that big a difference in a random read? :sarcastic: 
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