Status of SSDs under Fedora ?

Joerg Bergmann email at jbergmann.de
Fri Jun 11 09:58:05 UTC 2010


Am 11.06.2010 11:13, schrieb Andrew Haley:
> On 06/10/2010 11:19 PM, Phil Meyer wrote:
>    
>> On 06/10/2010 03:56 PM, Linuxguy123 wrote:
>>      
>>> On Thu, 2010-06-10 at 14:50 -0700, Konstantin Svist wrote:
>>>
>>>        
>>>> On 06/10/2010 01:53 PM, Linuxguy123 wrote:
>>>>
>>>>          
>>>>> I'm thinking of getting an Intel 160 GB SSD.   How would it work under
>>>>> Linux ?
>>>>>
>>>>> I'm using ext4 for that drive right now.  Is there a better filesystem
>>>>> for SSDs ?
>>>>>
>>>>> Is there anything that I should be aware of as far as switching ?
>>>>>
>>>>>
>>>>>            
>>> Have you run an SSD ?  Is longevity really an issue or is it folklore ?
>>>
>>> Thanks
>>>
>>>
>>>        
>> It is bot real and folklore! :)
>>
>> The fact is that any SSD, or other NAND type device has a limited number
>> of writes per address.  The real question is:
>>
>> "With your data needs and patterns, will you actually need to write to
>> the same address over 100,000 times?"
>>
>> For most people, that is a big fat NO.  The drives are smart enough to
>> re-arrange data around failed memory addresses.  So what happens most
>> often is a very slight decrease in available space over time.
>>
>> The advice given is just smart, because most file systems will update
>> the same physical disk 'block' containing inode data whenever a file is
>> accessed (atime).  The chances of that update hitting the exact address
>> every time is quite high.
>>
>> So, theoretically, if you just read a file on an SSD 100,000 times you
>> could destroy a single address location on the SSD.
>>      
> No, because all the SSDs you can buy today do some kind of wear levelling.
>
> Andrew.
>    
I use ssd disks on two machines for about 2 years, starting with fedora 9.
Both are SLC types, no problems until now. Starting with fedora 13, I have
included the discard option into /etc/fstab:

UUID=a33d1ae0-d527-4ce9-a1b2-7740a03adab3 /                       
ext4    discard        1 1
UUID=fe5a1b00-270f-4363-95f2-ba063b198019 /boot                   
ext4    discard        1 2
UUID=25e91a73-829e-4c13-80bb-90bd6f31aaf2 /home                   
ext4    discard        1 2
UUID=a08f6933-317d-4716-a064-65c0c47f7b66 /tmp                    
ext4    discard        1 2
UUID=0875ad5e-3f2f-4591-871a-fd33450f3ca4 /var                    
ext4    discard        1 2

Wear levelling is OK, but today ssd's should know the TRIM command which 
will
be enabled by the discard option in ext4. Looking forward to btrfs 
(maybe generally
recommended in fedora 15). btrfs is a copy-on-write file system which 
will avoid
writing a file twice on same physical position. Of course, btrfs 
supports the
TRIM command to.

Joerg


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