سرعة الرفع جيدة.

In Arabic, the present tense often uses a nominal sentence with no written or spoken word for is.

So:

• سرعة الرفع جيدة = The upload speed is good

There is no separate present-tense copula like English is here. Arabic simply places:

• the topic / subject first: سرعة الرفع
• the description after it: جيدة

If you wanted was, then Arabic would usually add a verb such as كانت.

It is an adjective, but in this sentence it functions as the predicate of the whole sentence.

So جيدة literally means good (feminine singular), and here it means:

• is good

This is very common in Arabic: an adjective can stand as the predicate in a nominal sentence.

So:

• الجو جميل = The weather is beautiful
• سرعة الرفع جيدة = The upload speed is good

Because it agrees with سرعة, which is a feminine noun.

The head noun of the phrase is سرعة = speed, and جيدة must match it in gender.

So:

• سرعة is feminine
• therefore the adjective/predicate is جيدة, not جيد

Even though الرفع is masculine, it is not the head noun here. The main noun is سرعة.

Because سرعة الرفع is an iḍāfa construction, often called a construct phrase.

In an iḍāfa:

• the first noun usually does not take الـ
• the second noun can make the whole phrase definite

So:

• سرعة الرفع literally means speed of the upload / upload speed
• even without الـ on سرعة, the whole phrase is definite because of الرفع

This is why Arabic says:

• سرعة الرفع
  not
• السرعة الرفع

They form an iḍāfa phrase:

• سرعة = speed
• الرفع = the uploading / the upload

Together:

• سرعة الرفع = the speed of uploading or upload speed

In grammar terms:

• سرعة is the first term of the iḍāfa (مضاف)
• الرفع is the second term (مضاف إليه)

A native English speaker often finds this easiest to understand as X of Y:

• سرعة الرفع = speed of upload

If fully vowelled in formal grammar, it is:

• سُرْعَةُ الرَّفْعِ جَيِّدَةٌ

Why?

• سُرْعَةُ is nominative because it is the subject/topic of the nominal sentence
• الرَّفْعِ is genitive because it is the second noun in an iḍāfa
• جَيِّدَةٌ is nominative because it is the predicate

In normal writing, these short vowels are usually omitted, so you just see:

• سرعة الرفع جيدة

Because ر is a sun letter. With sun letters, the ل of الـ is not pronounced; instead, the following consonant is doubled.

So الرفع is pronounced roughly:

• ar-rafʿ

not:

• al-rafʿ

A fuller pronunciation of the whole sentence with case endings is roughly:

• surʿatu r-rafʿi jayyidatun

In pause, learners often hear something closer to:

• surʿat ar-rafʿ jayyida

They are different structures.

• سرعة الرفع جيدة = The upload speed is good
• سرعة الرفع الجيدة = the good upload speed

In the first one, جيدة is the predicate of a complete sentence.

In the second one, الجيدة is an adjective describing the noun phrase, not finishing a sentence by itself.

So if you add الـ to جيدة, you usually change it from:

• a sentence meaning is good

to:

• a noun phrase meaning the good upload speed

Because سرعة الرفع stays together as one noun phrase: upload speed.

Then جيدة comes after the whole phrase to describe it.

So the structure is:

• [سرعة الرفع] [جيدة]
• [upload speed] [good]

Arabic adjectives normally follow the noun they describe, but here جيدة is not just modifying سرعة inside the phrase. It is describing the whole subject phrase as the predicate of the sentence.

Yes. سرعة الرفع is a normal MSA technical expression for upload speed.

It is commonly paired with:

• سرعة التنزيل = download speed

So in internet or networking contexts, this sentence sounds natural and standard.